Here’s our guide to setting up a basic, conventionally ventilated indoor garden on a budget. We’re going to show the different ventilation requirements for a 2 light and a 6 light grow in the same space.

Big rooms need lots of lights with a high-powered ventilation system whereas small rooms will only need a few lights with a low powered ventilation system. All sounds like simple stuff, doesn’t it? But how do you work out exactly what your room needs? Here’s what you need to consider:

Size

All of the equipment your new indoor garden will need comes down to the size of the room. So, the first thing you need to do is accurately measure it. You will need the length, width and height of the room.
The example shown has the dimensions of:
Length x Width x Height
24ft (7.2m) x 12ft (3.65m) x 8.2ft (2.5m)

Now before we get carried away filling this room with lights and fans, you have to consider the budget and ability of the grower undertaking this new project. A confident and experienced grower may well fill the whole room, but let’s not bite off more than we can chew. First, let’s create a smaller room within the larger room by sectioning off the back portion to give a working room size that is more suited to a beginner.
Length x Width x Height
12ft (3.65m) x 8ft (2.4m) x 8.2ft (2.5m)

You might well be asking, “What are the benefits of sectioning off the room? Why can’t I just hang the lights in the corner?” Well, by creating a room within a room you gain better control of the environment. With the sectioned off area you make the best use of the available light by having walls lined with reflective sheeting – this creates a bright well-lit environment for productive growth.

You can use various materials to section off the room but the better insulated, the better. A well insulated room will immediately lend itself to far easier environmental control.

If you have no interest in building your own indoor garden, or you’re not too confident with your DIY skills then don’t worry, help is at hand. You can purchase purpose-built indoor grow tents – highly recommended for all levels of grower! These come in many sizes, with one bound to suit your requirements, and it makes hanging lights, fans and filters a sinch.

Lighting

Now you know the size of the room you’re working with you can calculate how best to illuminate it. The most widely used light source for indoor gardens is high intensity discharge (HID). They are widely available, competitively priced and produce consistent results. Two types of lamps are able to run in HID systems; High Pressure Sodium (HPS) and Metal Halide (MH).
HID lighting systems are available in many different sizes, but the most commonly used for indoor growing are 1000W, 600W and 400W. Each size light is suitable for a defined amount of floor space:

1000W = 4-5ft (1.2-1.55m)
600W = 4-3.3ft (1.2-1m)
400W = 3.3-2.5ft (1-0.75m)

One thing to bear in mind is that the more powerful the light, the further away from the tops of the plants it needs to be. This means that if you have a low ceiling height, you should consider using lower wattage lights. The example room has an 8.2ft (2.5m) ceiling height so we can use the 1000W lights, as long as the plans don’t get bigger than 5ft (1.5m) which is fine for most plants. Indoor plants want to be short and wide to make the most of the light available. The distance between the light and the canopy that most growers follow are:

1000W = 39-31 inches (100cm-80cm)
600W = 31-24 inches (80-60cm)
400W = 24-16 inches (60-40cm)

Please bear in mind that the above information is for horizontally mounted lamps in normal open or closed reflectors. If you are using parabolic reflectors with vertically mounted lamps or air-cooled reflectors you can allow the light to be closer to the plants as there is less direct radiant heat.

So the floor space available in our room is 12ft (3.65m) x 8ft (2.4m). You could try and squeeze as many lights as possible into this room, but as well as being productive, you want to try and make your room easy and comfort- able to work in. To do this you will need adequate access around your plants to make maintenance and inspections easy. Approximately 2ft (0.66m) around your plants is a good working area. Elderly or disabled growers may opt for considerably more space than this. In our first example we’re using 2 x 1000W lights.

If you want to make life difficult for yourself, you could fit a maximum of 6 x 1000W lights. In order to make this room work you would need to choose a growing system or technique that allows you to move the plants to gain access around the garden. This might be achieved by growing in pots/containers or movable beds.

Ventilation

Ventilation in your indoor garden comprises of two main factors: the removal of hot waste (CO2 depleted) air and the input of fresh cooler air. Hot waste air is removed actively using an inline fan, AKA the extractor fan. Fresh cooler air can either be drawn in passively through vents or pushed in actively using another inline fan AKA the intake fan.
Now we know the size of the room, and the amount if light being used, we can now work out the ventilation requirements. In North America most inline fans are rated in Cubic Feet per Minute (CFM), whereas in Europe they are usually rated in cubic meters per hour (m3/hr).

The Extractor Fan

Firstly, we’ll work out what size extractor fan is needed. There are many ways to work out what size extractor is needed for a particular sized room, some equations are more accurate, others are overly complicated – the following method is very popular and straight forward and has served many growers well.

Required extractor fan size in CFM= Volume of active growing area (ft) x 1.25
Required extractor fan size in m3/hr= (Volume of active growing area (m) x 60) x 1.25

When we say the volume of the active growing area we mean the volume occupied by the lights and plants. To work out the volume simply multiply the length x width x height. In our example with 2 x 1000W lights this is 4ft (1.2m) x 8ft (2.4m) x 8.2ft (2.5m), which gives the volume of the active growing area of 262.4 cubic ft (7.2m3).

Once you have your volume, you need to multiply it by the amount of air changes needed per unit of time. For the majority of indoor gardens without AC or supplementary Co2, the rule of thumb is one air change per minute. For the CFM equation there is no need to multiply it as we already have the total volume in cubic ft which is needed to be changed every minute. For m3/hr equation we need to multiply the volume by 60 to step it up to the amount of air changes needed per hour.

Lastly, when using a carbon filter attached to the extractor fan we expect a drop in fan efficiency of approximately 25%. This figure is not fixed; it depends on the make and age of the filter and the length and course of ducting between the fan and filter and many more interesting factors that we won’t bore you with here. To step up this efficiency drop of 25% simply multiply by 1.25.

If we run this equation through our example indoor garden it gives us;
Required Fan size (CFM) = (Volume of Active Growing Area) x 1.25
(4 x 8 x 8.2) x 1.25 = 328 CFM

Required Fan size (m3/hr) = (Volume of Active Growing Area x 60) x 1.25
(1.2 x 2.4 x 2.5) x 60 = 432.
432 x 1.25 = 540 m3/hr

This final figure is the minimum size extractor needed. If the garden is in a very well insulted location such as a basement using this figure should be fine. If the garden is located in a very sun-exposed location such as an upstairs bedroom or attic then the extractor size may need to be increased by approximately 25%. More often than not, you will have to match your required extractor size to the nearest size avail- able. In this instance the nearest widely available inline fan size is a 6” (150mm) 390CFM (660 m3/hr) extractor.

Interestingly, if we work though the equation for the same room with 6 x 1000W lights it will give very a different answer;

Required Fan size (CFM) =  (Room volume) x 1.25
(12 x 8 x 8.2) x 1.25 = 984 CFM

Required Fan size (m3/hr) =  (Room volume x 60) x 1.25
(3.65 x 2.4 x 2.5) x 60 = 1314
1314 x 1.25 = 1643 m3/hr

In this indoor garden the nearest widely available fan size available is a 12” (315mm) 1000CFM (1700 m3/hr) extractor.

Oversized Fans

Many growers think ‘bigger is better’ when it comes to extraction but this is not always the case. By extracting air from the garden you’re removing the heat, but you’re also removing the hu- midity. This means that an oversized ex- tractor fan can often cause low relative humidity, which will create an onslaught of negative effects that will lead to poor plant growth.

‘Summer sized fans’ are also not always the answer to a warm indoor garden. There comes a point where it doesn’t matter how much air your extracting, if your incoming air is warm your room will stay warm. If you can’t keep the heat down and you’re changing the air in your garden more than three times a minute, you need to consider installing air conditioning or using air-cooled or water-cooled grow lights.

Fresh Air

As mentioned earlier, we need to get fresh air into the garden. This can be done using two methods:

1. By making passive vents (basically holes) through which fresh air can be drawn in.
2. By installing active inline fans that push fresh air into the garden.

When using passive vents you have to ensure there is adequate fresh air outside the growing area. It’s no good if you’re pulling in stale or warm air. This means you may need to have a window open so fresh air can be drawn in from outside and into the indoor garden. As a rule of thumb, the passive vents should be two to three times the size of the surface area of the extractor fan outlet. This means if the extractor has a 6” (150mm) spigot size, the garden will need 2-3 x 6” holes or rectangular vents with and equal surface area. When installing passive vents always have the extractor fan at the opposite end of the room. It’s better to have oversized passive vents than undersized. If the vents are too small, the extractor fan will struggle to pull in sufficient quantities of fresh air.

Indoor gardens with active intake fans often run more efficiently than those with passive vents. By pushing in fresh air you not putting as much strain on the extractor fan and you also get to choose where to pull the fresh air from. During the cooler winter months its best practice not to pump in very cold air, so a lot of growers pull slightly warmer air from inside their home. If it’s a room you spend time in, like your bedroom or living room, it will also have the added benefit of the air being slightly higher in Co2. During the summer months its best to pull fresh cooler air in directly from outside as air from inside you house is likely to be warmer. Whenever you pull air straight from outside it’s best to use an intake filter or ‘bug screen’ to limit the possibility of sucking in pests.
The golden rule when installing an intake fan is to make sure you’re blowing in less air than is being removed by the extractor. This creates a ‘negative pressure’ and ensures that all the air exits through the carbon filter. If you input more air than the extractor can remove the air will start to build up and cause a ‘positive pressure’ forcing untreated air out of the garden.
When selecting an intake fan it should have a maximum capacity that is 10-20% lower than the actual output of the extractor. This will maintain adequate negative pressure while not putting too much strain on the extractor and intake fans.
To work out the intake fan size we will need to take the extractor fan size and apply an estimated reduction for the carbon filter- 25%. If our target for the intake fan is 15% less air than the exhaust we need to multiply the reduced output by 0.85. Below is a work through of how to size up the intake fan for both or the example rooms.

2 light room:

Extractor size – 390 CFM (660 m3/hr)
Estimated extractor power with carbon filter – 390 x 0.75 = 292.5
Reduction to ensure negative pressure = 292.5 x 0.85 = Intake Fan Size 249 CFM (420 m3/hr)

6 light room:

Extractor size – 1000 CFM (1700 m3/hr)
Estimated extractor power with carbon filter – 1000 x 0.75 = 750
Reduction to ensure negative pressure = 750 x 0.85 = Intake Fan Size 638 CFM (1084 m3/hr)

When installing the intake fan, make sure the extractor is at the opposite end of the garden. It’s a good idea to split the intake air with a solid ‘T’ or ‘Y’ piece so that the cooler fresh air is distributed evenly. Using air socks or longer lengths of ducting with holes in is a good way of evenly distributing the incoming fresh air.
One last factor to consider is that inline fans are better at pushing than pulling air through ducting. This means than when positioning your intake fan, it’s better to place it nearer the source of fresh air and push it towards the indoor garden. To make the air reach the garden efficiently, make sure the duct runs are as smooth and straight as possible.

Air Movement

Moving the air within the garden is of utmost importance. A light breeze moving air over the plants’ leaves refreshes the CO2 depleted air, gets rid of heat and humidity and encourages transpiration. The area of an indoor garden where most unwanted heat will accumulate is between the lights and the canopy, so it’s absolutely crucial that this air is removed to avoid heat build up. To achieve good air movement between the lights and the canopy you can install fixed or oscillating air circulation fans. These can be wall mounted or floor standing and should be powerful enough to mix the air well, while not causing the plants to be blown too vigorously. You want to move the air, not your plants! If you point strong air circulators straight at your plants the air will move past the leaves so quickly that it will strip away the humidity surrounding the leaf and encourage rapid transpiration. This leads to the leaves losing water rapidly and can cause them to appear burnt at the edges crispy to touch; this is known as ‘wind burn’. If you need to enhance the air movement around your plants, it’s a good idea to point air circulators towards walls rather than directly at the plants to mix the air adequately while not causing the plants to be flapping around in turbulent wind.

Equipment location

To avoid unnecessary heat transfer, any equipment that generates heat should to be stored outside the garden. Most notably, the power packs (aka ballasts) that can get quite warm need to be situated outside the garden on a shelf or any non flammable surface. Having them outside the room also is best practice for electrical safety as they won’t be operating in a warm and humid environment and will not have risks of stray foliar sprays landing on them or accidental splashes of nutrient solution.
Nutrient solution will also benefit from staying outside the garden. Your reservoir will quickly heat up under the direct light from your grow lights so its best practice to locate your reservoir outside the garden.

Any liquid nutrients and additives should not be stored in hot or cold environments. It’s best to consult the packaging and see what the best environment is for your products but most appreciate a constant moderate temperature. This should again be outside your garden.

Summary

Following the above principles you can construct your- self a great, budget indoor garden, suited around you, while creating the ideal environment for your plants. All you need to do after this is choose a method to grow your plants whether it’s growing passively in plant pots, or using an active hydroponics system such as an Ebb and Flow, Drip, or NFT – all will flourish in your well planned indoor garden.

NEXT TIME:
We will be looking at selecting the best growing system to suit the needs of you and your garden and using fan speed and environmental controllers.

Have you ever been given this odd-sounding advice? Even when we are encouraged to try and understand how plants work, our inherent tendency to personify the natural world is inescapable. Growers often like to draw parallels between humans and plants, after all, there’s no doubt that plants are marvelous, highly specialized and well-adapted organisms. You might even go as far to say they are “intelligent.” But let’s be honest here. Plants are totally different from us, especially in the way they react and respond to their environment. However, if we can get our heads around the world from a plant’s perspective, we become what is commonly referred to as “green-fingered.” We become … better growers.

Have you ever wondered how plants “feel” humidity? An understanding of what humidity is, what it means to plants, and how you can manage it in your indoor garden will help you and your plants stay happy all year round.
The humidity of the air is basically the amount of water in the air. Water can only truly stay in the air when it is the invisible gas – water vapor. Small droplets of water in air, such as fog or mist, are not water vapor; they are simply larger particles of water temporarily suspended in the air that are ready to be turned into water vapor by evaporation.

Temperature plays an important role when it comes to humidity. The warmer the air, the more water vapor it can hold. This means the maximum amount of water that air can hold is directly related to the temperature of the air. As the amount of water air can hold constantly changes with temperature it is difficult to pin an absolute or fixed amount of water that can be held by air. So what’s the best way to quantify humidity if the goal posts are changing all the time? The answer is something called Relative Humidity (RH) – this is a measure in terms of percentage, of the water vapor in the air compared to the total amount of water vapor that the air could potentially hold at a given temperature.

Why is RH so important?

As growers we measure the RH of our gardens using digital or analogue hygrometers. These readings are very important because RH has a direct effect on the plant’s ability to transpire and therefore grow. Generally, plants do not like to lose lots of water through transpiration. Plants have some degree of control of their rate of transpiration through management of their stomata but the general rule is the drier the air, the more plants will transpire.
Now let’s move on to the idea of “pressure” – this is an important concept to grasp when it comes to understanding a plant’s response to humidity. All gasses in the air exert a pressure. The more water vapor in the air the greater the vapor pressure. This means that in high RH conditions there is a greater vapor pressure being exerted on plants than in low RH conditions. High vapor pressure can be thought of as a force in the air pushing on the plants from all directions. This pressure is exerted onto the leaves by the high concentration of water vapor in the air making it harder for the plant to ‘push back’ by losing water into the air by transpiration. This is why with high RH plants transpire less. Conversely, in environments with low RH, only a small amount of pressure is exerted on the plants’ leaves, making it easy for them to lose water into the air.

What is Vapor Pressure Deficit (VPD)?

VPD can be defined as the difference (or deficit) between the pressure exerted by water vapor that could be held in saturated air (100% RH) and the pressure exerted by the water vapor that is actually held in the air being measured.
The VPD is currently regarded of how plants really ‘feel’ and react to the humidity in the growing environment. From a plant’s perspective the VPD is the difference between the vapor pressure inside the leaf compared to the vapor pressure of the air. If we look at it with an RH hat on; the water in the leaf and the water and air mixture leaving the stomata is (more often than not) completely saturated -100% RH. If the air outside the leaf is less than 100% RH there is potential for water vapor to enter the air because gasses and liquids like to move from areas of high concentration (in this example the leaf) into areas of lower concentration (the air). So, in terms of growing plants, the VPD can be thought of as the shortage of vapor pressure in the air compared to within the leaf itself.

Another way of thinking about VPD is the atmospheric demand for water or the ‘drying power’ of the air. VPD is usually measured in pressure units, most commonly millibars or kilopascals, and is essentially a combination of temperature and relative humidity in a single value. VPD values run in the opposite way to RH vales, so when RH is high VPD is low. The higher the VPD value, the greater the potential the air has for sucking moisture out of the plant.
As mentioned above, VPD provides a more accurate picture of how plants feel their environment in relation to temperature and humidity which gives us growers a better platform for environmental control. The only problem with VPD is it’s difficult to determine accurately because you need to know the leaf temperature. This is quite a complex issue as leaf temperature can vary from leaf to leaf depending on many factors such as if a leaf is in direct light, partial shade or full shade. The most practical approach that most environmental control companies use to assess VPD is to take measurements of air temperature within the crop canopy. For humidity control purposes it’s not necessary to measure the actual leaf VPD to within strict guidelines, what we want is to gain insight into is how the current temperature and humidity surrounding the crop is affecting the plants. A well positioned sensor measuring the air temperature and humidity close to, or just below, the crop canopy is adequate for providing a good indication of actual leaf conditions.

Managing Humidity

Managing the humidity in your indoor garden is essential to keep plants happy and transpiring at a healthy rate. Transpiration is very important for healthy plant growth because the evaporation of water vapor from the leaf into the air actively cools the leaf tissue. The temperature of a healthy transpiring leaf can be up to 2-6°C lower than a non-transpiring leaf, this may seem like a big temperature difference but to put it into perspective around 90% of a healthy plant’s water uptake is transpired while only around 10% is used for growth. This shows just how important it is to try and control your plants environment to encourage healthy transpiration and therefore healthy growth.
So what should you aim to keep your humidity at? Many growers say a RH of 70% is good for vegetative growth and 50% is good for generative (fruiting /flowering) growth. This advice can be followed with some degree of success but it’s not the whole story as it fails to take into account the air temperature.

Humidification systems to increase RH.

Table 1 shows the VPD in millibars at various air temperatures and relative humidity. Most cultivated plants grow well at VPDs between 8 and 10, so this is the green shaded area. Please note that the ideal VPD range varies for different types of plants and the stage of growth. The blue shaded are on the right indicates humidification is needed where the red shaded area on the left indicates dehumidification is needed.

By looking at this example we can see that at 70% RH the temperate should be between 72-79°F (22-26°C) to maintain healthy VPDs. If your growing environment runs on the warm side during summer, like many indoor growers, a RH of 75% should be maintained for temperatures between 79-84°F (26-29°C.)

The problem with running a high relative humidity when growing indoors it that fungal diseases can become an issue and carbon filters become less effective. It is commonly stated that above 60% RH the absorption efficiency drops and above 85% most carbon filters will stop working altogether. For this reason it is good practice to run your RH between 60-70% with the upper temperature limit depending on your crop’s ideal VPD range, in the example it would be 64-79°F (18-26°C.)

The table also shows that if your temperature is above 72°F (22°C), 50% RH becomes critically low and should generally be avoided to minimize plant stress.
Please understand that by presenting this information we do not want you to go to your indoor gardens and run your growing environment to within strict VPD values. What’s important to take from this is that VPD can help you provide a better indication of how much moisture the air wants to pull from your plants than RH can.
If you want to work out for yourself the VPD of your plants leaves you can follow the steps below:

1. Measure the leaf temperature and look up the vapor pressure at 100% RH on table 2 below.
2. Measure the air temperature and relative humidity and look up the nearest vapor pressure figure on table 2.
3. Subtract the air vapor pressure from the leaf vapor pressure

Example:
Leaf Temperature = 24°C (100% RH)     Leaf VP: 29.8
Air Temperature = 25°C @ 60% RH     Air VP:     19.0
VPD=     10.8

Humidity’s Effect on Plants

Plants cope with changing humidity by adjusting the stomata on the leaves. Stomata open wider as VPD decreases (high RH) and they begin to close as VPD increases (low RH). Stomata begin to close in response to low RH to prevent excessive water loss and eventually wilting but this closure also affects the rate of photosynthesis because CO2 is absorbed through the stomata openings. Consistently low RH will often cause very slow growth or even stunting. Humidity therefore indirectly affects the rate of photosynthesis so at higher humidity levels the stomata are open allowing co2 to be absorbed.

Leaf roll on Thai basil- Localized humidity stress causes by the lights being too close.

When humidity gets too low plants will really struggle to grow. In response to high VPD plants will try to stop the excessive water loss from their leaves by trying to avoid light hitting the surface of the leaf. They do this by rolling the leaf inwards from the margins to form tube like structures in an attempt to expose less of the leaf surface to the light, as shown in the photo.

For most plants, growth tends to be improved at high RH but excessive humidity can also encourage some unfavorable growth attributes. Low VPD causes low transpiration which limits the transport of minerals, particularly calcium as it moves in the transpiration stream of the plant – the xylem.  If VPD is very low (95-100% RH) and the plants are unable to transpire any water into the air, pressure within the plant starts to build up. When this is coupled with a wet root zone, which creates high root pressure, it combines to create excessive pressure within the plant which can lead to water being forced out of leaves at their edges in a process called guttation. Some plants have modified stomata at their leaf edges called hydathodes which are specially adapted to allow guttation to occur. Guttation can be spotted when the edges of leaves have small water droplets on, most evident in early morning or just after the lights have come on. If you see leaves that appear burnt at the edges or have white crystalline circular deposits at the edges it could be evidence that guttation has occurred.

Guttation on tomato plants caused by high RH and wet coco coir.

Powdery Mildew from poor humidity control.

Most growers are well aware that with high humidity comes and increased risk of fungal diseases. Water droplets can form on leaves when water vapor condenses out of the air as temperature drops, providing the perfect breeding ground for diseases like botrytis and powdery mildew. If humidity remains high it further promotes the growth of fungal diseases. The water droplet exuded through guttation also creates the perfect environment for fungal spores to germinate inviting disease to take hold.

Quick reference chart:

So hopefully now you are not just ‘thinking like a plant’ – you’re ‘feeling it’ too!

Next time, part two of Plantworks will be looking at foliar spraying and how plants absorb nutrients into their leaves.

As we’ve learned in part 1 and part 2, in order to grow successfully in a hydroponic system, there are certain basics that always need to be kept in check: otherwise, plant performance inevitably suffers. After covering source water, nutrient and pH, world-renowned hydroponics expert Michael Christan breaks down the final ingredients of a healthy indoor growing environment: oxygen, light, temperature, humidity, air circulation and CO2.

Photos courtesy of AmHydro.

The 5 basics of recirculation and plant performance:

1. Pure source water
2. Balanced nutrient ions/anions (EC)
3. Optimum pH
4. Plentiful oxygen availability
5. Optimum light/temp/humidity/air circulation/CO2

The Importance of Oxygen

It’s obvious that loose, friable soil with organic matter and thriving microbes grows plants much better than tight, clay soil devoid of organic matter. The primary missing ingredient in the latter is air (oxygen) availability.

The air we breathe is composed of gasses: 78% nitrogen (N2), 21% oxygen (02), 0.9% argon (Ar) and 0.03% carbon dioxide (CO2). The one we’re focusing on in this article is oxygen. The action of microbes on organic matter in a loose soil produces air pockets as organic matter is mineralized. These oxygen pockets are crucial to the survival and rapid colonization of healthy microbial populations. When the organic matter in the soil is fully consumed by the microbes and plants have consumed all the minerals, oxygen becomes depleted and, if more organic matter is not reapplied, plant performance slows and pathogenic (anaerobic) microbes can colonize. This condition is best avoided.

In media-based recirculating systems, the O2 is in the media: e.g. rockwool, perlite, grow rocks. Plentiful air space is available even after water is drained from the media. Roots thrive in O2-rich pockets. They are able to produce prolific root systems and plentiful root hairs to increase surface area to better absorb available ions. This is the best reason for using media with porosity. Of course, flood and drain systems suck fresh air into the media when it drains, which is why it’s such a great irrigation system.

In water-based recirculating systems, NFT, DFT and Aeroponics, O2 availability is intrinsic to the design of the system. NFT is a flat-bottomed tube with a shallow nutrient stream moving slowly, keeping root hairs moist and absorbing O2 (see “NFT Gro-Tanks,” UGM009). Aeroponics is misting droplets of water, increasing the surface area many-fold for roots to grow prolific root hairs for ion absorption. It supersaturates the solution with O2. DFT uses air pumps and water temp to keep roots bubbled with 02 and oxygen rich.

The heart of a media-based or water-based recirculating system is the nutrient reservoir. This too requires oxygenation, especially when water temperatures rise. The use of air pumps and air stones on smaller reservoirs and pump-powered eductors (venturis) on larger reservoirs make a big difference in pathogen suppression (nasty fungi and bacteria don’t like O2). This agitation drives ethylene gas from the solution and increases the longevity of the nutrient. Be sure that, if there are reservoir lids, there’s room for air exchange with ambient air in the room or greenhouse. Many commercial growers use fresh outside air in their eductors to keep the nutrient solution optimum.

Dissolved Oxygen (DO) can be measured to determine solubility of oxygen in fresh water. Fresh water at 72°F (22°C) has a DO of 8.7 ppm; at 82°F (28°C) it drops to 8.1 ppm. Salt solutions are lower. As a rule of thumb, every increase of 1ppm in DO is equivalent to an 11°F (12°C) temp drop. The cooler the temp, the higher the DO. You don’t want cold water on plant roots, though. You want 72°F (22°C) water at your roots for most plants.

When we measured DO in our greenhouse reservoirs, we found that a 74°F (23°C) nutrient tank at an EC of 2 had a DO of 6.3 ppm (low because of salts and sitting still). When we turned on an eductor (venturi), which we do in ALL reservoirs, we received a reading of 7.6 ppm. BIG difference. That’s an increase of 1.3 ppm without changing temperature.

Then we add an in-line Mazzei injector in between the tank and the feeder pipe, which raises DO to 8.3 ppm. By the time the water had run down the NFT channel and 18 plants had their way with the O2, with some off-gassing occurring, there was an 8.1 ppm DO left in the nutrient solution going back to the reservoir. That’s what we’re after! Plants thrive at those DO levels. Makes ALL the difference.

Be careful: as water temperatures of salt solutions increase, you must mitigate by adding O2 in the reservoir as well as directly on the roots. If you can’t get the DO level up by mechanical means, then you will most likely require a water chiller, which is expensive but sometimes imperative. If you cannot bring water temps down or increase DO in the nutrient solution, your next action will be disease suppression or inoculating roots with beneficials to out-compete the pathogens that thrive in high temp, low DO water. If you do get a DO meter, get a good one. We use an Extech Model 407510.

Light

Photosynthetically Active Radiation (PAR) light is a fancy term for the wavelengths plants use to vibrate chloroplasts to power the engine of photosynthesis, a vaguely understood process in my opinion. It is said that PAR light is in the 400 to 700 nanometer wavelength range. No big deal if you’re outside or in a well-lit greenhouse. But if you are growing under HID light or using it as a supplement, it certainly is.

Color temperatures of lamps are measured in degrees Kelvin from a color rendering index (CRI). The blue/white side of the spectrum has higher Kelvin temp: 6000K-8000K (MH lamps). The yellow/red side of the spectrum has lower Kelvin temperature: 3000K (HPS lamps). As a rule, the higher the Kelvin temp, the more vegetative the growth. The lower Kelvin temps are used for supplemental and/or flowering light. Different bulbs have different combinations or blends of gasses for better PAR value. Plants can be finicky and prefer one blend of light more than another. Trial and error, sometimes, is the only way to find out what your plants really like.

High Intensity Discharge (HID) lamps produce light when the gases inside the fused alumina tube are heated to the point of evaporation by high voltage electricity. This process forces the metal gasses to throw off a barrage of photons partly in the PAR range. As the bulb burns over time, the metal gasses slowly change form and degrade out of the PAR range. It is not obvious, but plant performance can suffer from lack of the PAR light when there is no shortage of photons to the naked eye. To look at light as a possible limiting factor, keep track of the hours your bulbs have been burning. If you are over the recommended burn range as stated by the manufacturer, that could be what’s compromising your system. Rule of thumb with HPS bulbs is to replace them every 12 months, and MH bulbs every 9 months, with HPS burning 12 hour days, MH burning 18 hour days.

Outside it’s obvious what limits light, like trees. But in greenhouses, if the glazing is dirty, that’s a big deal and that situation just creeps up on you. Depending on what you’re growing and what time of year it is, a dirty film can cut out as much as 30% of available light. If you are using an 85% transmission film and have 30% attributed to dirt, that’s 55%, basically shade cloth. In situations where there is too much light and plants are unable to cope with the leaf temperatures or solar radiation, a white or metallic shade cloth is preferable to black, as black can radiate heat back down on the plant canopy. A simple mistake easily avoided by many growers in double poly greenhouses is that the inflation fan is pulling inside air in between the films, thereby creating moisture that blocks light. You can tell by the droplets in between the films, or a haze. It is always recommended to use outside air for inflation. Of course, all of this is dependent on location, latitude, geography, plant in cultivation and skill/experience of the grower. We cannot cover all those variables in a brief article.

Temperature

Plant response to temperature is pretty obvious. It’s visible. Plants stop growing when root temps hit 58°F (14°C). Air temp can actually be cooler than 58°F, but when roots are cool, growth slows and stops even when air temp increases. When temps are too high, say 95°F (35°C) plus, depending on RH, air flow, light, kind, size, and age of a plant, they may stop feeding and spend their energy evaporating water from their stomata to cool down. Temperature must be managed to keep plants transpiring and active in the sweet spot.

Most temp controllers are effective, turning on fans for increased air exchanges, but when temps are too hot outside, air conditioners must be used. As a variable, though, temperature control is straightforward. It’s common knowledge that insects like very consistent temperatures and no air movement. Find which temperatures are your best high and low, and vary them morning, daytime and night. Keep an inhospitable environment for the pests without sacrificing plant performance: another dance to master.

Humidity

The two ways of explaining humidity are relative humidity (RH) and vapor pressure deficit (VPD). Most people are familiar with RH and use hygrometers so, for the purposes of this article, I will use RH.

In my experience, this is the one variable that most growers need to be more aware of. The dance between temp/humidity directly affects transpiration rates as poor transpiration opens the plant organism to disease and mineral deficiencies.

RH is the amount of water vapor present in the air expressed as a % of the amount needed for saturation at the same temperature. Here’s what that means: if the humidity is too high, e.g. 95% at 75°F, plants cannot transpire or evaporate enough water to pull minerals up the vascular system even with stomata wide open. This usually results in calcium (Ca) deficiency (remember, Ca is a non-mobile element and must be constantly supplied to growing tips) and plant stress, which increases their vulnerability to fungal intrusion.

If humidity is too low, 50% at 75°F, stomata will open in an attempt to evaporate water because of the low pressure around the leaf, but then close up to conserve cell pressure in the leaf. Plants stress as they cannot take in CO2 with closed stomata and growth stops as the plant is just trying to survive without going into wilt (i.e. loss of leaf turgidity from which it’s difficult to recover). Again the plant is vulnerable to disease and insects. These two extremes points will create a high probability of crop loss.

As a rule, at 75°F (24°C), if RH is below 60% you must add moisture to get to 75% (which is ideal), but stay below 85% to avoid stress and disease. At 85°F (29°C), if RH is below 70% you must add moisture to get to 80% (which is ideal), but stay below 90% to avoid stress and disease. As temperature rises, air holds less moisture. Steer your plants within these parameters for optimum plant performance.

When RH is too low, use a fogger or humidifier coupled with outside air exchanges. When outside air is too warm and dry, you will have to use some form of air conditioner (if that is the only way) to drop the temperature to increase the moisture-holding capacity of the air.

When RH is too high, raise temperature to reduce moisture saturation of air coupled with outside air exchanges. If outside air has too high of an RH, you will need a dehumidifier to pull water out of the air.

Transpiration is king. Monitoring transpiration rates and keeping them optimum with temp/RH manipulation is crucial. If you are outside of the temp/RH safe zones and don’t use some mechanical method of bringing them under control, you will always be fighting the results of that variable being unchecked. This is where high quality environmental controllers come in handy

You can buy the most expensive nutrients, goodies and gadgets available to grow your crop, but if your plants are unable to transpire and you don’t know that, you had best learn quickly or get a day job

Air Circulation and CO2

No matter what kind of controlled environment you’re running, greenhouse or greenroom, air circulation is another key component that is often overlooked until mildew takes out your crop or your plants starve from lack of CO2. The great outdoors takes care of all this, but inside you have to provide the controls or fall prey to what you didn’t know you didn’t know.

Rule of thumb: 60 air exchanges per hour. Not only do you need to flutter your plants with gentle breezes from an oscillating fan or horizontal air flow (HAF) fans in a greenhouse, but you must freshen the air with air exchanges from outside, taking advantage of the 385 ppm ambient CO2. The raw materials that PAR light makes into carbohydrates are CO2 and H2O. CO2 furnishes the carbon and oxygen, while water furnishes the hydrogen for the carbohydrate (CH2O).

If air exchanges are frequent, 385 ppm CO2 is plenty unless you’re looking to accelerate growth by enriching your space with higher levels to, say, 1500 ppm CO2. Even if you are adding CO2, you still must exchange air. There are numerous ways to provide CO2: chemical reactions, gas bottles, gas generators and a variety of controllers and monitors depending on the size of the operation. For the purpose of this article, you just need to know that it is a basic component of the indoor growing environment, and be mindful that it’s always available. Without CO2, plants will not grow.

One of my teachers, Grenville Stocker in NZ, took me into one of his client’s lettuce/herb greenhouses and asked me, “Would you get a chair, sit down, read a book or hang out in here all day?” Actually, it was way too moist, not enough air movement, my shirt was sticky, and it was uncomfortably warm. I said, “No way.” He remarked, “How do you think those plants feel? The same way, I reckon, except they can’t leave.” Then he showed me powdery mildew in certain areas, a thrip infestation and tip burn in some of the lettuces. The plants did not look vital, they looked stressed. I noticed the HAF fans were down, because of a blown breaker that the grower had been meaning to fix for a week. He had an RH monitor but no controller to check humidity and spill air or add heat … AND he was doing only 1 air exchange per hour because it was cold outside. He wanted to keep temps up inside without turning on the heat, which would cost him money. I looked at the RH: it was 95%. Temp was 80°F but it felt like 90°F because of the humidity. His client was too busy to pay attention or take coaching, and he wasn’t even there. Grenville always tested me; he’d say, “What’s wrong with this picture?” Then he would point out a basic that was obvious once I saw it. Most problems were easy to correct once distinguished.

I found out later the grower lost 50% of his crop and the other 50% was barely marketable. Had he kept HAF fans working, increased his air exchanges and turned up the heat to drive off the humidity with the help of a controller, he would not have had crop and financial loss. Just that one error cost him a market: he couldn’t deliver, so a competitor moved in. The point I’m making is: don’t leave your plants in an environment you can’t handle being in yourself. Use meters and controllers, but always keep them honest by paying attention to what your skin says.

All the variables of light, temperature, humidity, air circulation and CO2 must dance together in a harmony that you must monitor and control to be successful and avoid crop loss. If you cannot distinguish which variable is out, you will be guessing what the problem is and perhaps taking actions that are detrimental. Next time a problem arises (which inevitably will happen) and you’re scratching your head as to what to do, go through this list and check off each one that you KNOW is in tolerance. These 5 basics could be what you didn’t know you didn’t know. Now that you do, dissect them and become competent with each one:

The 5 basics of recirculation and plant performance:

1. Pure source water
2. Balanced nutrient ions/anions (EC)
3. Optimum pH
4. Plentiful oxygen availability
5. Optimum light/temp/humidity/air circulation/CO2

For the content and experiences that allowed me to write these articles, I’d like to thank my teachers, Grenville Stocker (Stocker Hort), Jeff Broad (AutoGrow), Genaro Calabrese (ex partner), Grant Creevey (Accent Hydro) and all our clients and associates for sharing and being open to “figuring it out.” Controlled environment plant cultivation is infinitely beguiling; I am always learning a greater respect for being part of that process. Genaro’s motto: “Every plant, every day.”

Good luck and good growing.

Michael Christian, the president of American Hydroponics since 1984, is a hydroponic system designer and consultant to commercial growers worldwide.

Rockwool is a mainstay of commercial hydroponic growers – and for good reason. It takes up a minimal footprint and, when used correctly, yields like crazy. We asked Dr Lynette Morgan, a world authority on hydroponic vegetable production, to give us some expert advice on growing tomatoes in rockwool. There’s LOTS to be learned here as Dr Morgan takes us through how to develop irrigation strategies for your particular growing environment.

Rockwool, also known as stone wool or mineral wool, is the most widely used substrate for the commercial production of hydroponic tomatoes. It is also a great tool for smaller growers who can benefit just as much from its use in a range of different systems and situations. While rockwool is relatively easy to set up and use, it does require some monitoring and irrigation adjustment to make the best of its ability to hold high levels of moisture and aeration at the same time.

Rockwool originally started as a thermal insulation material in the construction industry: its lightweight but highly aerated nature helps keep heat in buildings, while being easy to handle, cut and install. However, towards the end of the 1960s, trials were carried out in Denmark to test the possibility of using stone wool as a substrate for plants. Things went well and since then rockwool as a growing media has seen some continuing development of the substrate and the tools used to manage it.

Rockwool comes in a range of sizes from propagation cubes to large slabs and even a granulated product.

Rockwool is manufactured by melting basaltic rock and spinning this molten mix into thin fibers which are then cooled by a stream of air. Although rockwool is a man-made substrate it is essentially made from rock and considered by many to be a natural product. Grodan dominates the rockwool market world-wide and is the most common brand used by large and small hydroponic growers alike. Grodan rockwool is highly advanced and is not a single product – growers can select from a number of different Grodan rockwool types such as `Grotop Master,’ `Grotop Master dry,’ and `Grotop Expert,’ all of which have slightly different properties and uses. `Grotop Master Dry,’ for example, maintains a slightly drier root zone and is used by tomato growers to steer crops away from overly vegetative growth. `Grodan Classic’ is used for multi-year use, while `Grotop Expert’ is designed for ultra quick root growth and development. Along with these product differences, rockwool of many brands comes in a huge range of sizes from tiny propagation plugs for seeds to larger cubes for cuttings, mega sized cubes for large plants, a wide range of slab sizes, and as a granulated product as well.

Setting up to grow with rockwool

1. Sit the rockwool down

Whether you are using the standard rockwool growing slabs, large cubes, or even pots of granulated rockwool, basic preparation is important. Slabs and cubes in particular need to be on a flat, even surface as any indentations will cause the material to sink and create pockets of unwanted moisture. Next, realizing that nutrient solution will be draining from holes cut in the slab’s plastic wrapper or from the base of cubes, some consideration for drainage of this solution away from the slab is important. There is no point in having well placed and made drainage holes if the solution can’t be channeled away from the slab and the material ends up sitting in a pool of stagnant waste nutrient. Many small hydroponic systems on the market these days designed for use with rockwool have trays and channels designed to do just this and these are a good choice for inexperienced growers.

2. Settle the rockwool in

Rockwool, whether it is slabs, small propagation blocks, or large growing cubes, needs to be prepared correctly by fully wetting the substrate before use. Some growers like to adjust the pH of their water to 5.5 before wetting up rockwool, but generally for small systems it’s not necessary with good quality brands (unless you have a very `hard’ water supply in which case acidification of the water before making up any nutrients would be a good idea). The rockwool should be fully saturated so that all of the material is wetted and then left to drain. Some growers pour water into the rockwool slab before the drainage holes have been cut to make sure everything has had a good drenching, while others just pour water on or run the irrigation long enough for saturation to take place.

3. Remember the holes

Rockwool slabs need drainage – holes or slits should be cut in the plastic sleeve the material comes in. Several cuts are required along the base of the slab. Granulated rockwool should be placed into containers or pots with plenty of drainage holes in the base.

4. Irrigation programs

The most common way of applying nutrient to rockwool slabs or large blocks is with the use of dippers. A simple drip irrigation system should use a dripper with a capacity of 2 litres/hour, with one dripper per plant. Because a standard rockwool slab may hold four tomato plants, four drippers per slab are required, which also means that if any one dripper becomes clogged, the entire slab will still be getting enough irrigation until the problem is fixed.

Developing an Irrigation Strategy for Rockwool – The Moisture Gradient

Rockwool is the most widely used substrate for hydroponic tomato production.

The irrigation program for any hydroponic plant is vital for successful growth, development and optimal yields. The most common problem experienced by smaller or new growers is over watering, and usually the grower is totally unaware that it is their irrigation program causing problems with plant growth. Flushing vast amounts of nutrient solution through the root zone in a substrate-based system often equates to plant murder – more is not necessarily better when it comes to nutrient application. This type of mistake is easy to make. After all, many new growers get enthused about hydroponics after seeing a well-run NFT or other solution culture system and assume that plants are more than happy to grow and thrive in a flooded root zone environment. However, solution culture and substrate systems are completely different and need to be managed in different ways for the plants to get the optimal root zone conditions they need. In NFT the roots should never be flooded: they sit in a very thin film of nutrient flow (2-3 mm or about 0.1″ deep), hence the roots have moisture at the base of the root system, but many of the other roots are sitting up in the moist air, accessing all the oxygen they need without being submerged. In a rockwool slab the plants are in a similar situation – at the base of the slab there is plentiful moisture, usually at media saturation levels, while in the upper layers of the rockwool slab the roots are in drier conditions and hence have access to plenty of aeration and oxygen for root uptake and respiration. It is this moisture gradient from the top to the bottom of the rockwool material that makes it such a good substrate. At the same time, growers who are not aware of this property can make the mistake of thinking the rockwool is too dry on the surface and over-irrigate their plants despite having plenty of nutrient solution being held deep down in the root system. Rockwool growing media, when being irrigated correctly, should not sit in a pool of nutrient and be completely saturated from top to bottom like a sponge. It is essential that the rockwool is allowed to completely drain so that excess nutrient leaves the slab or cube under the pull of gravity after being applied– in doing so, fresh air is drawn into the top layers of the material, providing fresh oxygenation for the root zone. By allowing the rockwool material to drain freely, over-watering becomes more difficult, although vast amounts of nutrient drainage from the base of rockwool slabs or cubes is not an ideal situation either.

Setting up an Irrigation Program

Obviously the amount of nutrient required is going to depend on factors such as the size of the plant, the growing conditions, light, temperature and, in particular, humidity, which drives plant transpiration and water uptake. So the irrigation program is going to change as the plants develop. Also an irrigation program needs to be developed and adjusted by each grower for their particular system, environment, and set up and this has to be monitored and adjusted as required. Just following guidelines for the amount of nutrient to apply at certain times will eventually lead to over or under-watering, as each plant and situation is different when it comes to nutrient and water requirements.

Commercial hydroponic rockwool growers have some good tools for fine-tuning their irrigation. The Grodan water content meter allows growers to measure the water content, EC and temperature in the rockwool slab root zone using hand-held meters or a continuous monitoring system hooked up to the computerized irrigation program. However, these sorts of high-tech tools are not often used by smaller growers and a successful irrigation strategy can be put together with just observation, some innovation, and a little time.

Remember the Moisture Gradient

Rockwool propagation cubes and slabs are designed to be used together to minimize root disturbance. Excellent moisture holding capacity and good aeration of the root zone are features of rockwool substrates.

Irrigation of rockwool is a little different to other solid substrates because of the way the material is manufactured to have just the right degree of moisture gradient, and because it does give quite a limited root zone for plants that eventually grow fairly large. For this reason, rockwool is best irrigated with short, frequent applications of nutrient, with just enough at each irrigation for the rockwool to reach ‘field capacity’. Field capacity is a term that means the substrate has drained fully but is still holding a good level of moisture for the plant roots to access until the next irrigation. At each irrigation, there should be some drainage from the rockwool material. However, this doesn’t need to be excessive. Even in closed systems where the drainage solution is being collected and reused, it pays not to over-water and not to run the irrigation continuously. Having around 10-15% of the nutrient solution fed to the plants, drain from the slab at each irrigation is considered to be optimal. This amount of drainage of solution flushes fresh nutrient solution right through the slab without too much wastage and usually keeps the EC in the slab fairly stable.

When rockwool is irrigated and allowed to drain naturally, it will then contain 80% nutrient solution, 15% air pore space and 5% rockwool fibers. A typical rockwool tomato growing slab actually holds around four gallons (about 15 liters) of nutrient solution immediately after irrigation, despite the drainage holes allowing free drainage of excess solution. Four gallons is a good reserve of moisture for four plants, so drying down to wilting point could take a long period of time for small plants.

How much solution should be given at each irrigation?

Having a drainage collection tray or channel under each slab allows growers to see how much drainage they are getting after each irrigation (even if this has to be poured off and measured in a jug) and the irrigation program can be increased or decreased to keep this at the 10-15% level. By doing this, the amount of solution to be given at each irrigation can be worked through and adjusted as the plants grow. Keep cutting back the irrigation amount until only 10-15% of the solution volume applied drains from the slab, and then the amount of irrigation has been fully adjusted for.

How often should nutrient be applied?

Rockwool needs small frequent irrigations, particularly under hot or low humidity conditions when the plants are taking up a lot of water. However, the frequency of irrigation can be as low as once per day (or every other day) for small plants under cool conditions, to over 10 times a day for large plants in a hot or dry environment. It can be hard to judge just how much moisture the rockwool material may be holding at any one time to determine when to irrigate. Smaller propagation blocks and even larger cubes can be gently picked up – the weight will soon tell you if the cube is saturated (it will be comparatively heavy and moisture will drip from the wet base), or whether it has dried out considerably, in which case it will feel very light (compare an unused dry cube to one in use). Rockwool is an unusual material in that, even when the slab has lost 50% of its moisture to plant uptake, the plants are still able to very easily keep extracting water until the slab is almost completely dry – so plants in rockwool can’t get water stressed until the rockwool is almost completely dry, by which time the cube or slab has become much lighter in weight. For granulated rockwool in pots or containers, a similar method can be used, either by gently lifting the pot to see what the weight might be (a light pot is a dry pot) or by a light tap or kick: if the pot moves, the rockwool has become quite light and potentially too dry.

Another method to try and gauge the moisture status of the rockwool and how often to irrigate is to carefully remove a small piece of the wrapper plastic and examine the moisture gradient of the slab from top to bottom. Like all growing media, moisture in rockwool can be gauged manually. Lightly touching or pressing the rockwool at the base of the slab will soon determine if there is still a good level of nutrient held in the base of the slab or whether it has become too dry. The top and middle layers of the slab should always appear drier than the base where the reservoir of moisture is naturally held, so only the base of the slab should be checked. Even if the top of the slab appears to be dry, this is not important as the moisture gradient has been designed to give these sorts of root zone conditions – only ensure the base of the slab has sufficient moisture.

This process of working out how much moisture is still in the rockwool material is not something that needs to be done for long. Growers will soon become quite skilled at working out their frequency and amount of irrigation for each stage of plant growth and may only need to do this for their first crop provided growing conditions remain stable. Other times when it might be important to have a quick check of the amount of solution drainage or amount of moisture in the slab is when conditions suddenly change – addition of more grow lamps, sudden changes in temperature or humidity, or rapid growth spurts can all change the irrigation requirements of the plants.

Generally, good brands of rockwool are quite forgiving compared to other substrates – the material is naturally well aerated and doesn’t suffer the compaction issues that some substrates do during the life of the crop. It does hold high levels of moisture, so the chance of drying out is not as severe as it might be with other substrates and being sterile gives young plants, seedlings and cuttings an advantage as well. The irrigation program and water holding capacity of the substrate depends on the fiber density and arrangement, which can differ from brand to brand.

More Advanced Irrigation Practices

With tomatoes and similar crops, growers have the option of using the EC and moisture content of the rockwool slab to help ’steer’ the plants into either more vegetative or ‘generative/reproductive’ growth, depending on what is required. Drying the slab back between irrigations and allowing the EC in the root zone to increase pushes tomato plants into a more generative or reproductive state with less leaf growth and more assimilate being directed into the fruit. A higher level of moisture maintained in the rockwool and a lower EC pushes the plants towards more lush vegetative growth. Skillful growers use these techniques to direct their crop and control leaf, flower and fruit growth at different times, and rockwool is a great substrate for this sort of control via the root zone.

Other Rockwool Tips

EC Levels and Management

Checking the EC in the root zone is important with rockwool just as it is with any media. The EC of the nutrient solution in the growing substrate changes as plants extract different ratios of water and nutrients from the root zone. The EC in the drainage solution coming from the base of the rockwool cubes or slabs is the best indication of the EC the plants are actually experiencing in the root zone. As a general rule, the EC in the drainage solution should be the same as or only slightly higher than that applied to the plants in the feed solution. If the EC is becoming much higher in the drainage than what was fed to the plants, then the EC in the feed solution should be dropped back – this is common under hot growing conditions when the plants might be taking up far more water than nutrients, hence concentrating the nutrient solution.

Rockwool Reuse

Rockwool for tomato crops can be reused – some commercial growers get many successive crops from rockwool slabs by steaming these after the plants have been removed and then replanting. Smaller growers can also do this – a few slabs can be heat treated by pouring hot water through them. Solarization is also possible, as is using chemical disinfectants, although care should be taken to rinse the rockwool well with plenty of water after using these. Commercial Grodan users have the option of the Grodan recycling service, which picks up the used slabs and recycles them into new product. However, smaller growers with just a few slabs of used rockwool can recycle the material by shredding it and reusing it as a growing media, as a component of potting mixes, or by incorporating it into outside soils and gardens.

Real World Rockwool Q&A

Q: What pH should I adjust the nutrient solution to and how do I monitor and adjust accordingly? For instance, keeping the tank pH at 5.8 and the run-off at 6.0 is perfect, but what happens if the pH starts to come back higher or lower than expected? What could / does this mean? And what should be done to correct it? How much should a grower raise or lower the pH of the tank with pH adjusters – when does a situation become ‘too extreme’ to use pH adjusters?

A: There are many factors that affect pH in the nutrient: some are normal like plant uptake and nutrient formulation salts (NH4 in particular), and some are not so good, like root disease. Water plays a big role and can range from very hard to very soft and hence needs to be handled differently depending on what a specific grower is dealing with. Chemicals for pH adjustment are also a huge topic! The nutrient solution pH is usually optimal at around 5.8 – 6.0 for commercial tomatoes; however, for small systems pH in the range of 5.5 – 6.8 is usually fine and having tight control at 5.8 is not necessary. The main problem with pH is with growers who might have a `hard’ water source, which is highly alkaline. In that case, acidifying the water with acid (nitric or phosphoric) before making up any nutrient will give better and longer term control of pH swings (in any growing media). pH should not need to be raised in most situations unless the water supply is very acid: in that case, potassium hydroxide should be used.

Q: I understand that rockwool can be prone to salt build-up if you don’t know what you’re doing like the commercial guys. Most hobby rockwool growers I have talked to flush either one day a week, throughout the whole grow and bloom cycle, or when they dump the res. (They will commonly give their plants 24 hours of either very low nutrient solution (if so, what EC?) or pure water, or even pure water with a product like GH Flora Kleen. What do you think of these flushing techniques? Do you have any better advice?

A: Rockwool is actually one of the better media for preventing salt build up as it tends to be drip irrigated from above and not bottom watered like with ebb and flow. Flushing is another subject that really needs a whole article to cover the theory, practice and problems with it. Flushing with straight water after a plant has been sitting at normal or high EC is not recommended: it causes the plant cells to suddenly take up huge volumes of water (because the osmotic pressure has been dropped in the root zone). This can cause cells to burst and create major physiological problems – splitting of tomato fruit is one common one; many other fruits and vegetables do the same. Even low strength nutrient can do this. Any changes in EC in the root zone should be done slowly (i.e over days), so a gradual dropping back of the EC over a few days should be done rather than flushing with water. Or better still, don’t let EC build up in the first place!

Q: What is the disadvantage of watering rockwool for a minute and getting 50% run-off in a closed system with adequate drainage, as opposed to watering for a minute and getting, say, 15% runoff? If you are only achieving 15% run off, is it not the case that the rockwool is already fully saturated and any additional runoff will just wash out the excess salts more thoroughly? In short, how difficult is it to over-water rockwool? I also can’t see what the problem would be for the plant if more run-off was created unless, of course, you were irrigating for several minutes to achieve this much run off, but even then surely the plant won’t feel any effect having its roots flooded for, say, 10 minutes, then allowed to drain freely?

A: Rockwool is a media which has been specifically designed for commercial growers who aim to have the recommended 10-15% run-off with the slabs spending as little time as possible at saturation levels – when doing this, the structure of the rockwool has been manufactured so that the root zone will remain at the correct moisture status which is why it is recommended. Also, with rockwool systems, the feed nutrient should be applied so that ‘excess salts’ don’t occur and therefore don’t need continual flushing. If the EC is getting high in the drainage solution, drop it back in the feed solution and/or increase the frequency of short irrigations. Rockwool, like any media, can be over-watered if flooded and is best kept below the saturation level for balanced growth.

Q. What’s the scientific explanation behind the influence that irrigation strategies have (or, to be more precise, the levels of moisture in the root zone) on generative / vegetative growth? Is this peculiar to tomatoes or is it applicable to other species?

A. Crop ’steering’ as it’s called is a technique used by commercial growers to manipulate the natural growth pattern of the plant. It’s widely used by skilled growers of tomato crops, but also on capsicum and many other plants as well. It’s quite a complex topic as there are a number of tools a grower can use in a controlled environment to direct the growth of the crop – commercial growers will use a combination of DIFs (day/night temperature differentials), EC, CO2, moisture control in the root zone and directional heating (i.e. directing heat towards the fruit or tops of the plants) to manipulate the growth of the plant. Different techniques force the plant to send the assimilate produced in the leaves into flowers/fruits when required or direct the plant back to some more vegetative growth if that was what was required. Various temperature techniques are sometimes used to keep seedlings or older plants as short and compact as possible (i.e. prevent stem elongation) and to get the plant to hold back on the production of overly large, succulent leaves. Commercial tomato growers use tools such as measurement of stem diameter to determine if their plants are getting overly vegetative or too generative at certain times of the year. The basic scientific explanation of why this works is that when a flowing plant encounters ’stressful’ conditions such a drying back of the root zone, high EC, high light and temperatures, it triggers a response – the plant wants to hurry up and flower, and to set seed to make sure it reproduces before the harsh conditions can kill it. We sometimes see this effect on lettuces which, under high light, temperature and moisture stress, can flower (or bolt) while the plant is still only a seedling and far from maturity. A plant with plenty of moisture under no particular stress is happy to go on producing a lot of large leaves with no hurry to set fruit and seed, which is great for vegetative crops such as lettuce but not so much with fruiting crops like tomatoes and capsicums. The ‘controlled stress’ commercial growers use to direct plants into more generative growth is often via the root zone because with Grodan rockwool very precise control of moisture content in the substrate can be controlled – particularly with the use of the Grodan moisture meter. And in hydroponics, control over EC is also fairly easy and precise. For this reason, Grodan Rockwool has different products for growers who might need to steer their crops towards more generative growth by having a drier root zone. It makes it much easier for the grower to then restrict irrigation and moisture levels in the root zone to steer the plants towards more generative growth and generally the technique is very effective. However, commercial growers use high tech tools likes moisture meters linked to their computerized irrigation program so that the crop is not at risk of being damaged by delaying irrigation to long. Smaller growers can certainly use similar techniques and allow the rockwool to run a little drier between irrigations and keep their nutrient run off to an absolute minimum if their plants are getting a bit too vegetative. Running a lot of nutrient through the rockwool on a frequent basis means the slabs or media are at saturation for much longer, and that favours vegetative growth (although we should also remember a lot of other factors, such as the growing environment, play in a role in the vegetative/generative balance as well).

Dr Lynette Morgan holds a B.Hort.Tech(Hons) degree and a PhD in hydroponic greenhouse production from Massey University in New Zealand. Her PhD thesis focused on hydroponic tomato production in both NFT and media systems and improvement of fruit quality aspects. Now a partner in SUNTEC International Hydroponic Consultants, Lynette is involved in many aspects of hydroponic production, including remote and on-site consultancy services for new and existing commercial greenhouse growers worldwide as well as research trials and product development for manufacturers of hydroponic products. Lynette is also the author of 5 hydroponic technical books: Hydroponic Lettuce Production, Hydroponic Capsicum Production, Fresh Culinary Herb Production, Hydroponic Strawberry Production and her latest release, Hydroponic Tomato Crop Production.

The basics – What is NFT?

NFT stands for Nutrient Film Technique. With this hydroponic system, plants grow in a purpose-built sloping channel with a fall of 1:40–1:50. Nutrient solution is pumped from a reservoir onto the channel where it passes over the plants’ roots and finally returns back to the reservoir. The roots on the channel develop to form a mat, which is partially in the shallow film of re-circulated nutrient solution, and partially above it. Utilizing this technique, the root mat growing in the nutrient film is supplied with essential water and nutrients, and the root mat above the film remain sufficiently moist with an abundance of oxygen.

The NFT system was developed between the 1960s and ’70s by Dr. Allen Cooper at the Glasshouse Crops Institute in the UK. In the early days, the growing channels were made in concrete floors. Today, growing channels are made from plastic and are often referred to as “trays” or “gullies.”

Why choose NFT?

Other than supplying your plants with the ideal root environment, NFT systems are incredibly efficient and environmentally friendly. The nutrient solution is recirculated for long periods: in some commercial applications, for many months. This continual recycling of the solution makes the most out of the water and nutrients you’re supplying. NFT systems also use very little growing media: just the small amount of substrate the plant is propagated in. This means that after each crop all you have to dispose of is a mat of roots, which easily biodegrades.

NFT Gro-Tanks

The system I will be demonstrating is called a Gro-Tank and is manufactured in the UK by Nutriculture.

The Gro-Tank is great for small-scale production as it has a wide top tray for the roots to grow on, with the reservoir directly beneath it spanning its whole length. A small submersible pump in the reservoir delivers nutrient solution to the tray above, which flows down the tray and back into the reservoir. This compact, self-contained design eliminates the need for lots of pipe work and is very low to the floor, making best use of the height available for tall/vining plants.

I have used the Gro-Tanks for many types of crops, including lettuce, basil, watercress, coriander, parsley, rocket, chard, chives, tomatoes, peppers, chillies, strawberries, cantaloupe melons, cape gooseberries, and many more. The diary below shows one of my NFT grows with cucumbers. I hope you enjoy…

Equipment

1 x heated greenhouse
1 x heated propagator
5 x starter plugs
5 x 4” rockwool blocks
1 x 604 Nutriculture Gro-Tank: 5ft x 1.5ft (153cm x 49cm) tray with 16 gallon (60L) reservior
1 x submersible adjustable pump
1 x submersible water heater
Spreader mat (capillary matting)
4 x roller hooks (plant supports)
Vine clips
Liquid nutrients and growth supplements

January 18th – Germination

I’m growing a cucumber variety called Carmen, which is an all-female F1 hybrid variety. The majority of cucumber varieties produce both male and female flowers; all we are interested in are the female flowers, as these develop cucumber fruit. This all-female (parthenocarpic) variety will develop a seedless fruit without the need for pollination. I found Carmen great last year for greenhouse growing as you don’t have to pick male flowers off and it produces large, full fruits.

I planted the seeds in starter plugs pre-soaked with a low-strength nutrient solution (EC 1.2) designed for seedlings and cuttings, and a liquid beneficial microbe additive. These were placed in a heated propagator and germination was fast!

Shown here is one cucumber seedling 8 days after planting. At this point they were transplanted into 4” rockwool blocks.

January 31st – Propagation

Considering it’s been 21 days since I planted the seeds, I’m happy with the way they’re progressing. They are now being watered with nutrient solution (EC 1.4, pH 5.8) every 2-3 days. The roots are doing really well and can be seen on the top of the block.

Without the block covers, algae would be taking over and the roots would not be growing so well on the surface. The natural light entering the greenhouse is being supplemented with 220W fluorescent strip lights. These plants should be ready for their NFT system in about 1 week.

February 4th – Growing on

The plants now need nutrient solution every day and the roots are clearly visible all over the bottom of the block. I also have increased the EC to 1.6. They will need to be planted in the next few days.

February 5th – Setting up

These cucumber plants are now 26 days old and are ready to go onto their final system, which will be an NFT Gro-Tank.

The most important thing about getting plants ready for NFT systems is to ensure they are well-established and have a mass of healthy white roots. Without this mass of roots inside the rockwool block, the plant will not be able to cope with the continuous irrigation of the NFT system. These plants have been propagated using an air pruning technique (see “Power Propagation” UGM0005) to ensure the rockwool block is packed full of roots.

This is the Gro-tank I will be using (below). It is called a 604. Nutriculture, which makes the system, also makes 5 other size variations to suit any grow area. The top tray is where the plants are placed and the reservoir underneath stores 16 gallons (60L) of nutrient solution.

The Gro-Tank has one delivery tube where the nutrient solution is pumped onto the tray using a small submersible pump with an adjustable output:

To ensure an even distribution of nutrient solution on the tray, I use capillary matting, aka “spreader mat.” The system manufacturers recommend using spreader mat and supply it with the system. One layer is enough. After laying it out, I fill the reservoir with water that has been standing in a storage tank for a few days: this allows some chlorine to be evaporated and, more importantly, allows the temperature to rise. Tap water in February in the North of England usually comes out ice cold and will seriously stress plants if used.

Once the tank is filled I turned the pump on and slow the output down so the solution lands in the middle of the first diamond. This provides a flow rate of approximately 1 quart (1L) per minute. Recommended flow rate for NFT systems can be anywhere between 13.5oz to 2 quarts (400ml to 2L) per minute. Determining flow rate in NFT systems usually depends on channel length; if you have very long channel lengths you will need larger flow rates. You could probably write a thesis on other variables that will determine the required flow rate for NFT, but I find that as long as nutrient solution flows as a shallow film and does not “puddle,” the plants grow well.

After a few minutes of the pump running, the spreader mat wets throughout the tray. I always run the pump and observe the way the water is flowing down the tray. I have found from experience that if the Gro-Tank is not placed on a level floor then some areas of the tray will develop puddles and other parts will remain dry. Leveling out the tank with thin pieces of plywood usually sorts out an uneven floor. Luckily, the floor is fine and I’m happy to “go with the flow.”

Now that I know the flow down the tray is perfect, I cut out the planting holes in the corriboard cover. Corriboard is twin-walled, semi-rigid plastic sheeting. It prevents any light from reaching the roots and can help provide a bit of support for the plants. I’m planting 4 plants in the Gro-Tank, so I cut the holes accordingly.

Providing support for large plants is very important. To support my cucumber plants I use roller hooks, which are a spool of string on a wheel attached to a support hook. The vines are trained up the string with the help of plastic vine clips. When they grow tall enough to reach the wheel, string is let out, which lowers the vine. This support hook is then moved along so the excess vine at the bottom rests on the corriboard. Using this technique, one of my cucumber plants last year was 49 feet (15m) long!

Another popular way to support plants on NFT systems is using netting, which is stretched out horizontally on a frame above the plants so that when they grow into it they are supported by the net.

Before planting onto the tray I remove the plastic wrapper from around the block. When I was learning how to grow using NFT systems I was told by a more experience grower at the time to “leave the wrapper on, otherwise the block will fall apart.” After a few crops I decided to experiment so I slid the wrapper up the block exposing the bottom third. This helped with initial establishment and root growth from the block, which I believed was a factor in achieving a more successful crop. The next crop I decided to risk it and remove the wrapper completely and, instead of the block falling apart, I got quicker establishment and a much better root mat. The block lasted the whole season, staying completely intact. Not surprisingly, I don’t follow this grower’s advice anymore.

Once the roller hooks are in place, I tie the string around the rockwool blocks and place them into position:

The positioning of the blocks on the tray is fairly important: I find staggering the plants works best. This allows the nutrient solution to flow uninterrupted through the mid-section of the tray, which helps once the root mat has built up. I also find that positioning the blocks so that the solution can flow through the grooves on the bottom of the block helps with establishment.

Then I place the corriboard and black and white sheeting back on the tray and lower the plants into their pre-cut holes. I cut the black and white with an X so the folds can be repositioned over the top of the block to cover it and prevent algae growth.

Now that the plants are in their system, I add a “grow” nutrient to the water in the reservoir at an EC of 1.6 and a pH of 5.8. I also add a strong dose of beneficial microbes to the mix to aid with root growth and disease prevention.

I put a submersible water heater in the tank and set the thermostat to 64°F (18°C). I also plugged in the pump, which I will now leave alone to run 24/7. Some growers plug their NFT pumps into a segmental or interval timer. This “pulse feeding” is not the strategy Dr. Allen Cooper conceived when he developed NFT, but some people growing plants with more sensitive root systems or who use large propagation blocks find it helps. It’s very important when implementing pulse feeding that the root mat never approaches a dry state. I have contacted Nutriculture about pulse feeding, and they only recommend that the pump is run 24/7.

These cucumber plants should settle in and start growing vigorously in the next few days. Hopefully I should be picking my first fruits in no time.

February 14th – Vegetative Progress

In 11 days these cucumbers on the NFT Gro-Tank have more than doubled in height and they are establishing well into their system. I have attached them to the string using plastic vine clips, which clip onto the string and hold the vine in place.

I have been routinely checking the nutrient solution pH and EC every 1-2 days. The pH was rising by 0.2 points every 2-3 days. As the pH reached 6.2-6.4, I added phosphoric acid to bring it back to 5.6-5.8. I like to let the pH drift a bit rather than keeping it within a tight range: as long as it doesn’t go higher than 6.5 or lower than 5.5, I’m not worried.

Usually I find the nutrient strength stays stable or increases slightly as the water level drops, but over the past 11 days the plants have used approximately 4 gallons (15L) of nutrient solution and the EC has dropped to 1.2. This is an indication that the plants are hungry, so I top up the reservoir with water and increase the nutrient strength to an EC of 1.8. Whenever I add anything to the tank I disconnect the delivery tube from the tray and submerse a larger 265 gallons/hour (1000L/hour) pump in the reservoir to mix the solution. Once the nutrient solution is corrected, I reconnect the delivery tube.

I always estimate how much water I add back to the tank and take a mental note. Once I know I’ve added back roughly the same volume as the tank holds (16 gallons / 60L) I will consider running the reservoir down to half full, emptying the tank, and refilling it with fresh water and nutrient solution.

Many growers change out the nutrient solution every week, regardless of how much the plants are using. I find this a bit unnecessary and like to base my solution change-outs on how the plants are using it.

The pictures below show how well the roots are extending from the rockwool blocks. Soon there will be a thick mat of roots all over the tray:

February 25th – Flowers and Fruits

It always amazes me how fast plants grow in a productive environment using hydroponic systems, but cucumbers are a whole other ball game. In 11 days they have more than tripled in size and burst into flower. One fruit is already quiet large and will be ready in a few days.

They have also started sending out tendrils and growing side shoots. I remove both but keep a few side shoots for cutting material and put them in my aeroponic propagator.

The greenhouse environment is pretty easy to maintain this time of year. The heating keeps the night-time temperature around 64°F (18°C) and the top vents ensure the day temp does not exceed 77°F (25°C). I have 2 centrifugal humidifiers running to keep the relative humidity between 60-70%.

The plants are now using 1.5-2 gallons (6-8L) of nutrient solution per day and I make sure I top up the reservoir frequently. It’s better to have a full tank as it provides a better buffer for changes in pH and EC. The plants seem happy with the nutrients at 1.8 EC so I’ll leave things be.

One thing I love about NFT is that you don’t have to think about irrigations. The pump is on a slow trickle, and that’s all that matters.

The cucumber fruit develops behind the un-pollinated female flower.

February 27th – Nutrient tweaking

We have had a few warmer, brighter days recently and the plants are loving it. The first large fruit is growing well but is showing signs that I need to tweak the nutrient slightly. You may notice in the picture below that the bottom of the cucumber is slightly more bulbous than the top. The leaves of the plants are also showing a faint yellowing (chlorosis) around the edges. This is a sign that the plant requires more potassium.

To increase the potassium in the solution I add a blooming additive high in potassium and phosphorus at the rate of 1 ml per L. Before adding this I top up the tank with water, add the PK booster, then add more base nutrient to bring it back to 1.8.

You may also notice some loose vermiculite on the tank and floor. I have introduced the predatory insects Phytoseiulus persimilis, which come in a vermiculite carrier. I noticed a small outbreak of spider mite on some peppers on the other side of the greenhouse, so as a precaution I sprayed all the plants in the greenhouse with a natural-contact insecticide that works by suffocation, not chemicals. A few days after spraying, I introduced the predators to clean up any lingering spider mites. I will now introduce a bottle of 2000 Phytoseiulus persimilis every 4 weeks throughout the greenhouse and keep spraying to a minimum.

February 29th – Roots going mad

The roots are really growing well now and starting to develop to form a mat in places. I like to regularly inspect the roots in the NFT system, mainly because you don’t get to do it with other systems!

March 3rd – Plant Training

The plants have now reached the full height of the greenhouse so I let out a small amount of string and lower the vines.

Once I have lowered these a few times I will move the roller hooks clockwise around the Gro-Tank. The stems rest on top of the corriboard. I started using this training technique with my tomatoes and tried it with cucumbers. I find it works pretty well but most commercial growers implement an umbrella training system. I have yet to try it but will get around to it one day.

March 11th – New plants!

The side shoots I took off 2 weeks ago are now rooted plants and are ready for transplanting.

I have to say, aeroponic propagators are great. I have one running continuously in the corner of my greenhouse and just put shoots in and forget about them. 1-2 weeks later you have cuttings. Can’t get any easier.

March 14th – The Bumper Crop

The plants have definitely responded well to the PK booster. The leaves are now dark green all over and the fruits have developed to be large, full and evenly shaped. Some are slightly curved but it adds to the character!

I’ve had 3 cucumbers off the plants so far, but today I picked 6 ripe fruits in one go. From here on out I guarantee I will have so many cucumbers that I will make myself and all my friends sick of the sight of them!

March 26th – Growing on

The cucumbers have been growing well and are now producing ripe fruit at a steady rate of two to three cucumbers every four days. They could try and produce more but I remove developing fruits once there are more than 4 developing on each vine. If there is a high fruit load on the plant, developing fruits will abort. The weather is starting to warm up and the greenhouse is now thriving from the increased day lengths and light intensity. Bring on summer!

Looking Ahead

Recognizing the environmental conditions and adjusting the nutrient solution is part of my ongoing management strategy for recirculating systems. As warmer weather comes along in May and June I will certainly see the EC rising every few days in the reservoir. As this starts to happen I will dilute the EC slightly to around 1.6.to compensate.

Water uptake will certainly go up too so I will have to make sure I regularly top up the reservoir once a day. I also make sure I service my pump every 2 months. This is fairly quick and easy to do and will give me peace of mind that it’s in good working order.

Interested in NFT and want to learn more? If you missed Everest’s introduction to NFT and grower’s tips in UGM0009, check it out here!

Javan Kerby Bernakevitch, a permaculture designer and teacher-in-training, introduces us to the principles and practice of permanent (agri)culture.

“Permaculture is revolution disguised as organic gardening.”
- Graham Bell, from Permaculture – A Beginner’s Guide

Permaculture is not organic gardening, and I am not a gardener. What I am is a permaculture practitioner who uses organic gardening, and many other tools, to design systems that work to water, feed, warm, house, and provide community, not to mention: make a garden.

So if permaculture isn’t just gardening, then what is it?

Permaculture is not the rain that falls, nor the roof that collects it or the catchment systems that stores it. Permaculture design is the relationship between these things. Permaculture is the match maker, creating passionate love affairs between rain and plants, humans and animals, and ultimately achieving systems that produce enough natural resources to provide for their own maintenance and reproduction.

Rainwater collection.

Imagine a ball that drops, hitting a lever that turns a wheel pulling on a string attached to a light bulb. Each step creates the necessary conditions for consequent steps which eventually will turn on the light bulb. Similar to well set-up dominoes. We can learn the skills to design whole systems that are focused on goals and fixing problems at the source, instead of focusing on the symptoms.

A backyard graywater filtration system that takes the sink, shower and washing machine water from the house, passes the water through a strainer, and then filters it through this man-made wetland bedded in 4 bathtubs that irrigates the gardens directly. Those irrigated beds produce 10-20% more than the non-graywatered beds.

Graywater filter.

With the light bulb glowing over your head you might have realized that practicing permaculture is not all that difficult. In fact, you probably are practicing it already and don’t realize it. Why? Because the knowledge contained under the umbrella of permaculture is not new; it combines the ancient and traditional knowledge of growing food with the modern science of ecology and new technology. Work in permaculture is self-evaluating: either it works or it doesn’t. The beauty of this movement is that, if you can learn from your errors, you can learn to design systems that work. You don’t have to wait for a committee to stamp your certificate or a teacher to baptize your understanding through tests.

“If you’re a scientist, you could liken it to a miraculous wardrobe in which you can hang garments of any science or any art and find they’re always harmonious with, and in relation to, that which is already hanging there.”
- Bill Mollison, the godfather of permaculture

Permaculture is a way of looking at the systems that sustain us, and designing them to have built-in endurance and sustainability to gain the highest output from the lowest input. It is not just the organic garden: the garden is just a piece of the bigger picture. A picture that includes the local climate, site topography, water access and drainage, capacity of the land and its users, where income is produced to finance the whole process and a host of other items. It is looking at the pieces of life and designing systems that produce the basic necessities needed to sustain and provide joy while creating rich, wealthy lives.

“Wealth is a deep understanding of the natural world.”
– Inuit definition

“I think it’s pointless asking questions like ‘Will humanity survive?’ It’s purely up to people – if they want to, they can, if they don’t want to, they won’t.”
- Bill Mollison

Bill Mollison, a disgruntled and highly motivated biologist, culminated a true “aha” moment with student David Holmgren in 1978 when they set out the seminal work Permaculture One. Coined as a combination of the words permanent and agriculture, and then permanent and culture, permaculture from its textual origins is about creating a world were we can live indefinitely. In this work, Mollison and Holmgren articulated their thoughts on sustainable living through a positive action movement in which anyone could be involved. The publication helped to create the first texts for the personal educational keystone of the movement: the Permaculture Design Certificate (PDC). Any keeners out there will be able to find PDC courses being offered in online and hands-on formats.

“If people want some guidance, I say, just look at what people really do. Don’t listen to them that much. And choose your friends from people who you like what they do – even though you mightn’t like what they say.”
- Bill Mollison

Contrary to the parental adage “do what I say, not what I do,” Mollison urges those interested to watch and see what is really happening. In a way, that’s how permaculture started. Working in wildlife relocation, Mollison realized that a forest needs no watering, weeding, fertilizing or other “outside care.” The forest is self-perpetuating. Mimicking the ecological principles he observed in the forest, he conceptualized that he could “make a system” that could produce food for human consumption. In essence, a food forest. This self-described “revelation” was understanding that there are beneficial interactions between living and non-living components. As people, we can assemble those components together to create beneficial connections and yields.

When Mollison asked an elderly Greek woman in a vineyard why she planted roses among her grapes, she replied: “Because the rose is the doctor of the grapes. If you don’t plant roses, the grapes get ill.” Accustomed to science, this answer did not sit well with Mollison. He began to research and found that the rose produces a certain root chemical that the grape root uptakes, which in turn repels the white fly (a pest for grapes). The story is the same from both Mollison and the woman’s perspectives: the grapes grow in community with the roses. However, the understanding behind the story changed. This story is where permaculture can be understood: in nature, organisms work in relation with one another. And using our commonsense we can observe these interactions, work out the commonsense or scientific understanding of what is happening, and reassemble the principle behind the interaction to create systems that feed, clothe, house, warm, and provide us with community.

Now in its fourth decade, the permaculture movement has spread like wildfire, creating a global grassroots community. Global in scope and adoption, permaculture has been able to specialize to meet specific needs. As permaculture is not an ideology, but rather an idea, it can change and adapt to any situation. In Haiti, permaculture practitioners were on the ground shortly after the earthquake, providing safe drinking water and human sanitation with a fraction of the budget of other aid organizations with twice the results. These efforts have grown from solid ethical building blocks that help guide the intentions of practitioners. These ethics, in order of priority and importance, are: Earth Care, People Care and Fair Share.

Earth Care

“We are sufficient to do everything possible to heal this Earth. We don’t have to suppose we need oil, or governments, or anything. We can do it.”
- Bill Mollison

“The Earth is a living, breathing entity. Without ongoing care and nurturing there will be consequences too big to ignore.”
- David Holmgren

Humanity has withdrawn so much of the natural capital from the earth’s savings account that we are no longer living off the surplus interest; we are now eating into the capital itself. We’re living on the savings, and they’re running low: it’s a lot like college without the getting-more-educated bit. From the north to south pole, to the tip of Mt. Everest and the bottom of the ocean, our environment is degraded and degrading at an alarming rate (imagine 1,000,000 fire alarms going off in a closed phone booth and you’re close to how serious the situation is). Synthesized chemicals at toxic levels can be found in every environment, in newborn children, and even in pollen (121 herbicides, fungicides and insecticides at last count); these are the very building blocks that support life.

Think of it this way: if you were hospitalized and depending on a medical life-support system, would you jiggle the plug, poke holes in the feeding tubes or pour toxic waste in the IV bag? Not unless you’re Keith Richards or a cockroach, and even then I think they’d both think twice about it … at least the cockroach would.

Earth Care is the top priority. Earth Care is our top priority. As a curmudgeonly 63 year old farmer from Manitoba advised, after I asked what I should grow on a certain piece of land…

Me: “What should we grow here-”

Him (cutting me off): “Soil.”

Me (frustrated but respecting my elder): “Right, I understand that, but in this micro-climate, what would be good to propagate-”

Him (cutting me off again): “Soil.”

Me (realizing there might be something he’s trying to tell me): “Okay, so you’re saying I should grow…”

Him (finitely stating): “Soil.”

At present, our greatest threat to humanity is not climate change (though that affects soil loss), nor pollution (this does affect soil loss), nor deforestation (now, that really affects soil loss). Our greatest threat is … soil loss. Without healthy ecosystems, soil is destroyed. Without soil, there is no food and, without food, the chairs around our global table become vacant. And it gets rather lonely sitting by oneself.

People Care

“I cannot save the world alone. It will take at least three of us.”
- Bill Mollison

Me, myself and I. Okay, and you too. And you can join, and … well heck, let’s invite everyone to the party. After ensuring that our life-support system is tended to, we turn to each other realizing that if the entire human species is on a planet with finite resources then we in turn all affect and effect each other. Like it or not, we are all in this together. In a closed system, the actions of one are felt by many, detrimental or beneficial alike. In permaculture, and life, everyone has something of value to bring to the party.

In a scarce economy, resilient employees embody the same strategy that ecology demonstrates: an organism that places itself in the most service to the whole, survives. We can see how helping friends and family survive supports our personal survival, and we may evolve a matured ethic that sees all humankind as friends and family and thus life itself as our ally. People care then turns into species care and we too have the “aha” moment that Sister Sledge had: “We are family.”

Fair Share

Remember kindergarten? No, not the dirt eating (which thankfully we don’t have to resort to … yet), but the idea of sharing. Well, sharing is back in style, sharing is the new khaki. With a new twist, fair share is also about abundance. Surplus is created either through an extraordinary amount of effort, which turns into a deficit of time and energy, or by limiting consumption. By conserving resources and setting limits to consumption, we can set our best course for survival to include others while creating the conditions to further the two ethics above.

The Prime Directive of Permaculture

“The only ethical decision is to take responsibility for our own existence and that of our children.”
- from The Permaculture Handbook, by Bill Mollison

Under the prime directive of permaculture, the three ethics (Earth Care, People Care and Fair Share) guide us to devise methods of applying them to our gardens, land, economies and nature. We can see permaculture as “the mechanism of mature ethical behavior, or how to act to sustain the earth” and our existence on it.

Well, if this hasn’t blown your mind yet then strap in for round two … how to go about applying and practicing intentional permaculture. From the prime directive and the ethics we spiral outwards to principles, strategies and, finally, techniques. These three are the holy trinity of permaculture in action.

Principles

Principles are beneficial as there are no penalties for error, only learning from errors, thereby leading to new ideas and methods. Now, here’s where the idea of permaculture being open-source really gets going: at a recent permaculture teachers’ training session, the facilitator (a long-time permaculture practitioner and teacher) stated that she knew of over 372 principles related to the movement. 372? Yup, 372. And by the time you start practicing permaculture, I’m sure you’ll have come up with a few more, or remember one that your grandma used to use. My Ukrainian Baba used to bellow from the top of the stairs when my brother and I were rough-housing: “Smarten up or I’ll throw you out, one by each!” The humor (or maybe it’s the genius) of this maxim lies in the translation to English: those parts that do not work with the overriding ecological principles at play (like my Baba’s patience, or the ability of the earth to absorb the pollution we are producing) are “thrown out, one by each.”

As you move further down this rabbit hole you’ll find many principles. However, I found permaculture best sampled like a good buffet, in sizable portions. David Holmgren, the other author to the first book of permaculture, continued down his own path and has produced some excellent work, including 12 concise principles that are easy to remember and to implement. Some of my personal favorites of his are:

Integrate Rather Than Segregate

The three sisters. Photo credit: Abri Beluga.

This principle has always wowed me by providing concrete examples of how to integrate plants together in communities or guilds that provide for the needs of other plants. The traditional example in North America is the “three sisters,” or maize (corn), beans and squash. Benefiting from each other, the maize provides the structure for the beans to climb (no poles needed). The beans fix nitrogen for the soil and the other plants, while the squash vines spread along the ground, blocking the sunlight that weeds need. The squash leaves are also a “living mulch,” creating a microclimate that retains moisture while the prickly hairs on the vines help deter pests. This guild integrates while utilizing the “waste” of the other plants, thereby touching on another great Holmgren principle: Produce No Waste (meaning that everything can have a use, even if we call it “waste”).

The Mollisonian Permaculture Principles that stand out for me are:

Work With Nature, Rather Than Against It

The revolutionary Masanobu Fukuoka (you’ll thank yourself if you read his The One Straw Revolution) once remarked, “If we throw nature out the window, she comes back in the door with a pitchfork.” When insecticides are used, the predatory insects (insectivores or cannibals, as I like to call them) are wiped out with the pests, ensuring that if an explosion of pests proliferate next year there will be no predators to keep their populations in check. Consequently, more insecticides are sprayed, tipping the scale even more. All pests are never killed and the survivors’ resistance is bred into a new generation, riding nature’s pitchfork aimed right at our food crops.

Visible through this window in the south side of a cob building is a frost peach growing on Vancouver Island. Peaches are not typically grown on Vancouver Island, but this tree is thriving because of the heat absorbed by the structure and the resulting microclimate.

The Problem is the Solution

Everything works both ways. It is only our perspective that judges a thing to be beneficial or not. If the south side of the greenhouse is constantly facing the sun, construct that side out of glass or plastic (salvaged, if possible) and, as the north side never receives sun, let’s construct that side out of a substance that has thermal mass (think of it like a thermal battery: it can up-take heat and return the heat to the surrounding area) like rock, cob (a traditional building material made up of clay, sand and straw), or something else that absorbs solar heat.

A greenhouse with south-facing glass and a north cob wall to retain heat.

Moving swiftly along strategies, like the ones below, are just like a handy number two Robertson screw driver or your Felco pruners: a tool to aid you on your permaculture journey.

When designing any site, be it a garden, a house, or even a driveway, here are the first three things to consider, in order:
1. Water
2. Access
3. Structure

1) Water – No matter where you travel or what you do, water is where the chemistry of life occurs. It’s also where some of your biggest headaches or joys can come from. First, consider where your water source is. Is it close to land that has a lot of sun in all seasons? What’s the land like around the water source? Where does it recharge from (underground, a stream that comes in from your neighbors’ property, precipitation)? Next, where does the water go? Does it drain on the land? Is that drainage seasonal or consistent year-round? If water is life, understanding the nature of your water on-site can save thousands of hours and just as many aspirin or cups of willow tea.

2) Access – As people, we design systems to water, feed, warm, house and provide us with community. If we design those systems first and then go to design access, we may find that the 6′-wide bed is too big for us to garden from the side. Considering how much a system will have to be “bumped” up against informs our decisions on how and where to construct that system. For example, chickens (the official permaculture mascot) need daily feeding (input) and collection of eggs (output). As keepers of this system, additional time and strain is endured if the chicken coop is placed far away from the house. Thus, if a system is “bumped” up against constantly, then placing that system closer to where we are increases the yields (outputs) while decreasing the work (inputs). This also applies to pathways, driveways, and other forms of getting to and away from systems.

3) Structures – Now that you know the water is draining on the north side of the hill and the best vehicle access is from the south, siting your structure can be made by an informed decision. In North America 40% of all energy consumed is by building and maintaining structures. With such huge amounts of resources inputted into your structure (house, greenhouse, tool shed), it’s important to site your structure where water is accessible and not threatening, and access is easy and not labor intensive.

“Permaculture is the end of the lawn virus, symptomatic of consumer culture.”
“You could say it’s a rational man’s approach to not sh*tting in his bed.”
- Bill Mollison

Or perhaps the definition is: “it’s sustainability, distilled, served straight up.” Or maybe it is just understanding that silver bullet solutions are best left to werewolves, proving that silver bullets are as fictitious as their intended fantasy targets. Catch-all solutions like pesticides and magic pills always have unintended side effects: it’s best to address the problem at its source.

As Geoff Lawton (the architect behind the Youtube video “Greening the Desert” — worth the time to watch) says, “All life’s problems can be solved in the garden.” Maybe permaculture is all about organic gardening … however, you’d do well to discard the definitions and just go out there and continue to garden, add in a sprinkle of permaculture, and be fruitful and mulch apply.

Javan Kerby Bernakevitch is an environmental educator, professional communicator, facilitator and editor. An O.U.R. Ecovillage resident on the West Coast of British Columbia, Canada, Javan continues to expand his knowledge and passion for sustainability through permaculture as a designer and teacher-in-training.

Join the discussion on how to incorporate permaculture principles into the indoor garden: post your comments and questions below!

WORDS: Brett McCormick, William McKenzie, and Alec Mayall

This hydroponic greenhouse is designed to feed four families with fresh produce throughout the year. With the collective financial investment and sweat equity of four different families, a shared greenhouse an easy way to connect with friends, family and/or neighbors and help the environment by cultivating your own food. Initial costs might seem high, but with a properly built structure and some TLC you will be able to cut your trips to the store down exponentially. Not only will you be saving money in the long run, you will know what you are consuming. In this issue we’ve chosen a 12’x24’ structure to demonstrate what type of facility would be needed to produce enough lettuce, bell peppers, tomatoes, and cucumbers for four families throughout the year.

(Click to see a larger image.)

Budget

There are many different types of greenhouse structure kits on the market today. You can find kits for greenhouses this size for around US$500. This would be a simple kit, only providing building materials for the actual structure. Other kits for this size of greenhouse range in the $2,000 to $4,000 range. These structures will provide you with a more aesthetically-pleasing greenhouse with better ventilation. Much of this budget is dependent on how technically inclined and handy you are. For practicality purposes, we will figure that the four families in this collective will complete all of the work, therefore minimizing the labor costs.

A conservative budget to get your hydroponic greenhouse fully up and running will be around $5,000 to $8,000. Many of these kits don’t supply a foundation, hydroponics systems, electricity, water, and many other factors that go into this budget. The further distance your greenhouse is from utilities (e.g. electricity, water), the more expensive it will be to run them to the greenhouse. When considering your budget and which features you’d like to include in your hydroponic greenhouse, remember that it is always easier to add internal features than it is to add size to your greenhouse.

Site Location & Preparation

When selecting a site it is important to ensure there is ample sun for the majority of the day. It is essential to have an open spot where the skies are clear to the east, west, and south. If you are unable to have completely clear skies facing these directions, you will reduce the maximum plant growth in your greenhouse. A little shade is acceptable, as this is a family-run project and you are not building a greenhouse for commercial production.

When considering the site for foundation preparation you should ensure that the site is level. As mentioned earlier, greenhouse kits don’t come with foundation kits, although most of them will tell you how to prepare a foundation. One simple solution is to use treated 4”x6” wood for your foundation. It is important that, while fastening these together, the foundation remains square and level. You can fasten these with decking screws or, even better, galvanized lags that will penetrate connecting wood to at least two inches. Anchoring your foundation is very important. To do this you can drill half-inch holes every 3 feet in the 4×6 and pound 24” rebar into the ground. You want to make sure that the rebar is flush to the wood so that they won’t get into the way of the actual greenhouse structure. Also, ensure that your foundation is slightly above grade.

Preparing the Floor

For your flooring, you want to use something that will drain easily but that is also easy to walk on. A simple option is gravel. Before you lay in the crushed rock, you want to ensure that you lay down black ground-cover fabric to ensure that all weeds are kept out of your ideal environment. It will actually benefit you if you lay this down before the foundation is set up, because otherwise the weeds will enter in through the corners of the foundation. The next steps are to secure the greenhouse to the foundation. From here you can follow the instructions of your greenhouse kit.

What’s for Dinner?

For this greenhouse, tomatoes, bell (sweet) peppers, cucumbers and lettuce are being grown.

Tomatoes

Tomatoes are started in 4” rockwool and are placed on rockwool slabs so the roots have more room to grow. The slabs are wrapped in plastic, so it is important to cut slits in the plastic to allow excess water to leak out. The slabs are placed directly onto the gravel so they can drain well. They are top fed from drippers. If you want more insulation under the rockwool slabs, you can put foam underneath so they aren’t touching the ground. This is not completely necessary, but it can help control the temperature of the root system. The rockwool slabs are 3’ long and can house 5-6 tomato plants. Each tomato plant will produce around 20lbs of fruit each season. You will need to train the young tomatoes to grow up onto a trellis system so that the plants can support the fruit. Rockwool is a good choice because tomatoes’ root systems can thrive in the small space and don’t need as much volume to be effective. As well, tomatoes are annual plants so you can spend the extra money for the rockwool as the rockwool will suffice for the entire season. Rockwool is a proven media for tomatoes and will promote vigorous growth. The tomatoes are planted in September and are pulled in July. This gives you time to clean out the greenhouse and start fresh for another year of crops.

Cucumbers

Cucumbers are started in 4” rockwool cubes and are grown in 5-gallon pots, two cucumbers per pot. Coir is the chosen medium for this because it is cheap, effective, and it is a byproduct, so we are preventing waste. Also, with coir you have the option to treat and re-use it for the next growing season. The cucumbers will need a trellis system to support them when they start to produce cucumbers. They are top fed through drippers from the main nutrient reservoir. In this greenhouse there are 20 cucumber plants: you can expect to produce 20-30 cucumbers per plant each season.

Peppers

Just like the cucumbers, the peppers are planted in 5-gallon pots, with coir as the grow media and a top-fed dripper system. You can expect to produce about 20 peppers per plant each season.

Lettuce

The lettuce is grown in a NFT system: it is the most effective technique for growing leafy greens, because lettuce has such a fast turnaround. The only media needed for this system is the media that you propagate your seeds in. You can either buy or make a NFT system. There are five 4”x4” troughs with 10 growing sites in each trough. The troughs should be placed about 4-10” apart, depending on the stage of growth that the lettuce is in. With this system, you should be able to crank out at least 10-15 heads per week or about 250 per season, depending on how you set it up and if you are constantly propagating and have a cycle going. In hotter months you can expect to cultivate your heads of lettuce in about 8 weeks, from seed to final product. It will take about 13 weeks in winter months. This will need a separate nutrient reservoir, which is constantly circulating. The troughs are set up on a slight slope so that they drain back into the reservoir. Make sure that you have the reservoir covered so that you don’t have a build up of algae.

Grow Environment

Ensure that you have vents on either side of the greenhouse for proper ventilation. Put screens around the vents to guarantee that no pests enter your greenhouse through these vents. Keep in mind that a very fine screen will inhibit proper airflow. One solution is to build a box wrapped in a fine screen so that there is more surface area for the air to pass through. Also, install multiple oscillating fans to ensure proper air movement.

The desired temperature is 65°F (18°C) at night and 75-80°F (24-27°C) during the day. The better quality polycarbonate product used will make heating and cooling easier.

If you have good air movement in your site, simple vents will suffice at moving air around your greenhouse and cooling it. The most consistent way to cool your greenhouse is with an electrical fan, pulling in cold air and pushing out the hot air. Another economical way to cool your greenhouse is to have an evaporative cooling system. This works very well in areas of low humidity and high temperatures. For areas with higher humidity and lower temperatures, it isn’t as effective. An evaporative cooler will be able to lower temperatures by 5-7°F (14-15°C). A last resort to cooling is using shades. They are are sold in different colors and densities, but the white fabric is the most effective cooling shade for the light that it cuts out. Usually they are applied in the spring and are taken off in the fall when the temperatures start to drop.

Good Green Builders was founded in December of 2009. It’s a first-of-its-kind general contracting company that specializes in the construction of indoor hydroponic grow rooms. Based in the San Francisco Bay area, GGB offers a complete line of services and equipment to accommodate the needs of anyone who desires to have an indoor garden.

How many people can you feed with your indoor garden? Share your tips, tricks and lessons-learned below!

There are a lot of CO2 generators on the market, varying by capacity. Connecting either a propane or natural gas line, a generator burns gas to produce CO2. When the burner is on, CO2 is generated. When it’s off, not.

Controlling this with an electronic CO2 controller will avoid wasting gas and create the exact environment of your choice.

Alternatives to using a gas-burning CO2 generator include the yeast/sugar soda bottle method (very imprecise) or a CO2 tank with a CO2 regulator.

Hydro Innovations’ MiniGEN is a compact CO2 generator and comes in at 6″x7″x10″. It’s small and adorable. Like Pikachu, small packages can generate powerful results.

Included accessories

– AC adapter
– 2 small screw hooks to screw into the top of the MiniGEN (for hanging)
– 2 worm-gear hose clamps for the water-cooling hose bibs
– 2 mounting screws for mounting the unit against a wall or wooden support
– 12-foot gas line with regulator for your propane tank

Setup & Installation

– Connect the included gas hose to the MiniGEN and a propane tank.

– Either hang the MiniGEN via its included screw hooks (good metal ones, too!) or flush-mount the unit against a wall. I opted to use ratcheting rope hooks with the screw hooks, but standard light chains would be fine.

– Plug the AC adapter into the MiniGEN and then into your CO2 controller.

– Slide the water hoses onto the hose bibs. The water hoses slide easily onto the front hose bibs for the MiniGEN. Cinch down the connections with the included worm-gear clamps and you’re good to go. I only wish that all of Hydro Innovations’ gear used these hose bibs. Easy on and easy off.

– For added measure and because I am paranoid, I teflon-taped the MiniGEN water hose bibs. As a former Boy Scout, I believe that added safety breeds security. No exception here—albeit the directions specifically state that these measures are not required.

Operation

Once everything is connected, your CO2 controller takes care of the MiniGEN.

The MiniGEN does have an on/off switch. Prior to walking away from your installation, ensure that you turn this on. The switch proves very handy when working around in your grow room. No need to waste CO2 with your grow chamber open—flip the switch to ‘Off.’

One exception to using a CO2 controller. If you are using CO2 as a natural pest-killer (around 10,000 PPM), you won’t use a CO2 controller. OR, you’ll use one that allows you to specify 10,000 PPM as an acceptable level.

Not only will this eradicate all pests in your grow room, you may eradicate yourself if not careful. Show extreme prudence if you attempt this sort of CO2 application.

Performance

Once connected, the MiniGEN takes a few clicks (of the electronic ignitor) to light the propane. I watched the CO2 controller. Two minutes later, the indicator crept from 500 PPM to 1500 PPM CO2 and turned off the burner. The MiniGEN’s burner generates 1.5 cubic feet/hr of CO2.

My grow chamber is 4′ wide, 3′ deep, 7′ tall. I hung the MiniGEN slightly above my light reflector and laid the CO2 controller slightly beneath the plant bases—approximately 3 feet between the two. This way, I ensured that at least 1500 PPM CO2 flowed across all levels of the plant tops.

Heat

A common issue with CO2 generators is heat. Pure and simple, fire is burning the propane to generate your CO2. Fire = heat. What to do with it?

The good folks over at Hydro Innovations solve that problem with all of their CO2 generators by water-cooling the units. Using a water chiller and pump with the MiniGEN, my grow room sees no added heat—at all.

If you’re running the MiniGEN without the water cooling (which you can do), you will need to add some sort of environmental cooling (ala conventional air conditioning or via a Hydro Innovations IceBox setup).

Safety

For being such a small unit, the MiniGEN incorporates two cool safety features:

– The electronic ignitor turns on only when CO2 is to be generated. No pilot light. Not only does this eliminate an unnecessary active fire in your grow chamber, but it conserves gas.

– An anti-tip sensor will not allow the ignitor to trigger if the unit is not level. If the unforeseen happens and the MiniGEN falls down or tilts, the unit will not fire.

How to make it better?

For once, I’m stumped.

The only suggestion that I can offer is a visual indicator of propane flow. I have not run out of propane yet. When I do, the only indicator will be the constant clicking of the MiniGEN’s ignitor. If I’m on an extended trip, this might last several days.

A visual indicator of either the flame or the gas (flowing/not flowing) might work well. However, on the MiniGEN itself, this would be less than ideal because you would need to open your grow room to see the indicator. Instead, the included 12′ propane hose should be substituted for one with a flow indicator on the tank side.

Other than that, this is a simple, perfect little beast.

Conclusion

If you have a grow room on the medium to small size (10′ x 10′ x 10′ or smaller) or otherwise don’t need super-fast CO2 flow, the MiniGEN is YOUR CO2 generator.

Simple. Cool. Efficient. Safe. Enough said.

Happy Gardening,

Curtis

We asked Kevin Anderson, a veteran indoor gardener in B.C., Canada, to give us his tips on how to handle transplants the right way.

So, What Exactly Are We Talking About?

Alrighty then. All you gorgeous growers out there will no doubt be familiar with the task of starting lots of seedlings or cuttings in propagators, perhaps in rockwool cubes or small seedling trays filled with growth media. Some of you may use those fancy cloning machines too – all well and good. But, sooner or later, it’s time to move your young, developing plants on to the next stage: a larger pot or a hydro system (e.g. ebb and flood table). This is called ‘transplanting.’

Crowded, leggy tomato plants, begging to be transplanted!

Transplanting is often considered the second most stressful event of a plant’s life, cloning being the first; however, there are many things we can do to minimize or even eliminate this stress.

True – much of the stress caused when transplanting is through delicate roots getting damaged as the plant is removed from its original pot and relocated. However, young plants more commonly suffer because they are placed under high intensity lighting too early. It’s not so much about how delicate your fingers are … it’s more about sudden changes in growing environment.

Before you remove the plant from its existing pot, prepare the new medium and be sure the environment is forgiving (more on this later). If transplanting to an inert medium (one that is devoid of nutrients, e.g. soilless mixes, coco coir, rockwool, and expanded clay pellets) it’s important to pre-load the medium with some nutrition. For cuttings this should be a fairly weak nutrient solution with an EC of 0.8 to 1.2 and for more mature plants 1.5 to 2 depending on species and size of plant.

For peat moss based soilless mediums, simply water until it is saturated with your own fertilizer mix. A good tip is to try adding some seaweed extract, which contains natural plant growth regulators / hormones that help stimulate root growth and reduce transplant shock. Always make sure your water / nutrient solution temperature is 68°F (20°C) to avoid shocking the roots with cold water or depriving them of oxygen with water that is too warm.

For rockwool simply soak the cube or slab as normal with the correct strength solution at a pH of 5.5 – 6.0 and a temperature of 68°F (20°C) for 24 hours, and then drain off the excess nutrient solution.

It All Comes Down To … Timing

For optimal results it’s important to transplant at just the right time. For clones this is when they have been fully hardened off and preferably have plenty of air-pruned roots showing from the cube or pellet. For more mature plants this is when the roots have fully filled the pot or cube but haven’t become root bound. To check if a plant is ready, gently squeeze the edges of the pot so the plant will come out with little effort. If you can see an abundance of roots just starting to creep along the edge of the pot, but they haven’t yet begun to fully circle, you are ready to transplant. If the soil or loose growing media starts to fall apart and there aren’t many visible roots, the plant is telling you that it needs a little longer in its current home before being transplanted.

One step at a time! Make sure not to transplant from a small pot to a very large pot as the medium will stay wet for too long, discouraging the roots from searching out water – this can lead to drowning and dampening off in severe cases. Potting up in stages also helps to produce a dense root mass. As a rough guide for many fast-growing vegetables, freshly rooted cuttings and seedlings will thrive if they are transplanted from a 2” to a 1 gallon sized pot and later into a 2-5 gallon pot. Be careful not to overwater new transplants as this will retard root development.

Here’s an important tip for growers who start off their cuttings / seedlings in rockwool and then move on to a soilless mix: be careful! Why? Because the soilless mix will wick water away from the rockwool and dry the cube out before the roots have ventured into the new soilless medium. You may find that you have to water the newly transplanted clones well before the soilless mix has dried because the cube itself is bone dry and houses most of the clone’s roots.

With a hydroponic medium like rockwool the same basic principles apply. A plant should be placed on a slab or into a larger cube when many roots are beginning to poke out the bottom of the existing cube. You can pull the plastic wrapper aside and check to see if there are plenty of roots showing. Again, you don’t want them to be circling the cube.

You really need to take care when removing the young plant from its original pot or seedling tray. Take your time. Gently squeeze around the root zone to loosen the plant from the pot. If transplanting from a seedling tray, try a gentle pinch at the bottom of the root zone – this pushes the seedling out of the tray easily.

If using loose growth media, place it lovingly into a pre-dug hole and gently backfill the hole and consolidate the media around the plant. Be careful not to compact the media (especially if using soil) when you back-fill the hole, but make sure you haven’t left any large air pockets. Then lightly water again to really settle the media around the newly-transplanted specimen.

Environment for Transplants

Okay, so we’ve been gentle and moved our seedlings or cuttings into their new homes. What about the growing environment? How can you tweak this to allow the plant the easiest transition possible? Remember, the aim of the game here is to give the roots an easy time so they can focus their energy on growing and extending their network, rather than all their energy being monopolized with supplying water and nutrients to a struggling plant.

Newly transplanted cuttings or seedlings hate hot and dry conditions. Too much air movement will increase stress too, by forcing the plant to transpire more than necessary. An unforgiving environment will force the young root system to work hard, just to keep up with the transpiration through the leaves. The trick is to keep humidity levels high (70-80%) and gradually wean them to levels around 60%. Humidity plays a HUGE part in determining how hard the roots have to work, so keeping the humidity at around 70-80% for the first few days using humidity domes or Victorian Bell Cloches is a great way to maintain higher humidity levels around single plants.

Domes and cloches can be removed for increasing periods of time to allow your plants to gradually acclimatize to their new vegetative environment.

Temperature should be kept at no more than 75°F (24°C) and no cooler than 70°F (21°C): the warm temperature will help ease the plant through the transition.

Blinded by the Lights

During this delicate transition, don’t go overboard with the lights! It’s so easy to get carried away and get over zealous in the early stages. Remember, the more light you give your plants the more the roots will need to spend their energy supplying the plant with water and food for it to utilize this light. Not a bad thing when you have a large established root system, but just after transplanting it is much better to allow the plant time to establish its roots rather than putting them to work at full tilt.

It’s common for indoor gardeners to move their plants from a fluorescent T5 fixture to a metal halide. Suddenly your plants are receiving far more light and enjoying lots more space than they had in the propagator or seedling tray. It doesn’t matter how delicately you handled the transplantation: young plants simply cannot keep up with the huge demand a high intensity grow light puts on them, especially in a demanding environment. The droop you will inevitably see is simply a symptom of the roots being unable to supply the plant with enough water in order to keep up with its demands. As with everything you do in the indoor garden, it is important to make changes slowly and gently, easing plants into more demanding environments as softly/gently as possible. Clones in particular should be broken into the more intense lighting conditions as gently and gradually as possible.

To minimize shock, always raise HID grow lights at least 4-5 feet above the plant for 1000 Watt bulbs and 3-4 feet for 600 watt bulbs. I know, I know – the lights look way too high, but I assure you this is enough light for the young plants to photosynthesize and, crucially, it doesn’t put too much strain on the root system. Dimmable ballasts work great here as you can save energy by simply dialing back on the intensity. After a few days and once you see the emergence of new growth you are safe to start increasing the ballasts back to full strength and / or lowering the lights.

Got a transplanting tip you want to share? Do you have a particular product or technique that you swear by? Share your wisdom by posting a comment below!