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.

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.

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!

WORDS: Heather Walker

Germination Basics

To go from seed to seedling, tomato plants need a moist growing medium, light, and warmth. I grow seedlings in my own organic potting mix of peat moss, vermiculite (some growers prefer perlite), green sand, bone meal, and organic soybean meal. You can add some aged compost too, but weeds may take over your seedlings if the compost wasn’t hot enough to kill the weed seeds. I soak the mix in a wheelbarrow with warm tap water (we’re on a well, so no chlorine worries here) then run the hose to add water until I can squeeze the soil mix and water runs out. I fill 4-inch pots with the wet mix, then plant one seed in the center of each pot and label it: name, date planted, open pollinated or hybrid.

I like to start my tomato seeds in 4-inch pots on the windowsill in my living room, directly above a baseboard heater: the additional bottom heat gives them that extra encouragement. This summer was the first year I tried heat mats, and I definitely noticed a shorter time to germination with those bad boys.

To know when to water, dig down an inch or so at the edge of the pot, and if it’s still moist then don’t bother watering. If it starts to look dry, soak the pot a few times with room-temperature water.

Eager tomato seedlings on a heat mat.

Seedling Mix

2 parts by volume sieved garden soil
1 part by volume sieved sphagnum moss
Add to each cubic foot (5 gallons) of mix:
1 cup agricultural lime or dolomite lime
1 cup cottonseed meal or soybean meal
1 pint soft rock phosphate or 1 cup steamed bone meal
1 cup kelp meal

From “Growing Vegetables West of the Cascades,” by Steve Solomon.

The Sprout

Once the sprout emerges with its first pair of leaves, it’s time for the tough love. If you spoil your tomatoes when they’re young, they will grow into leggy plants that will be ill-prepared for the real-world conditions in the outdoor garden. If you give your tomatoes lots of warmth when they aren’t getting a lot of sun or supplemental light, they can get “leggy,” growing tall with a spindly, weak stem. This is particularly important for growers in the Northern half of our continent, where the sun’s strength and height in the sky in March/April may not offer enough light. The plant, receiving lots of warmth but not much light, reacts as if it’s being shaded by other competing plants: as a result, it grows fast and tall in an attempt to access the sun and out-compete the other plants that it thinks are crowding it.

These leggy tomato seedlings were exposed to too much warmth with not enough light, which encouraged them to stretch: the stems are thin and weak as a result. Weak plants are more susceptible to disease, drought, and pests. Photo: Greg Wagoner.

To prevent leggy tomatoes and encourage stocky, strong growth, narrow the gap between the light and heat the plant is receiving. To do this, steel your heart and move every tomato with leaves into an unheated greenhouse during the day, unless it’s unusually cold. The greenhouse protects the young plants from the wind, cold, and rain/snow, but exposes them to cooler temperatures than in the house, and more sunlight through the poly-plastic roof and walls: they will receive more light and less heat than on the windowsill or heat mat. Bring them in at night until you’re confident that the temperature won’t drop below 50°F (10°C), which can compromise a tomato plant’s development or kill it.

Ideal Tomato Growing Temperatures

Day: 65-70°F (18-21°C)
Night: 50-60°F (10-16°C)

It’s also important to expose your tomato seedlings to air movement from this point forward. Fans, ventilation, an open window, or even your hand brushing their tops a few times each day will encourage more stocky growth and prepare the plants for the realities of wind. Novice growers often leave the clear dome on their plant starts for far too long. Don’t be an overprotective tomato parent!

Transplanting

It’s very likely that your tomato plants will outgrow their starter pots before it’s safe to plant them outside. In fact, this is preferable: the more times you can transplant your tomatoes into larger pots, the better. Why? Because every time you re-pot a tomato plant, you bury it up to its “neck” (just below its top set of leaves), or as much of the plant as you can fit under the soil. The tomato will then send out roots from the newly-buried stem, creating a more well-developed root system. And a strong root system leads to a healthier, more productive plant! Transplanting in this way also helps control the ultimate size of your plant once it’s ready to go into the garden: it’s far easier to plant a foot of stem and foliage with 8-inches of well-formed roots than a 2 foot spindly monster that will snap in half if you look at it funny.

So once your tomato outgrows its four-inch pot, bury the plant up to its neck in a gallon pot of soil, with the top set of leaves above. If you start your tomatoes in 1-2″ cell trays, transplant them into 4-inch pots when they’re ready for more room, then eventually into the gallon pots. And once a tomato outgrows its gallon pot, it’s probably time to plant it outside.

Transplanting a tomato plant from a small pot to a larger pot: bury the plant up to its neck, leaving the top set of leaves above the soil.

Hardening Off

It’s a blue-skied, warm, sunny day: you’re ready to unpack those shorts and plant out your tomatoes! But hold on. It’s crucial that you gradually prepare your tomato plants for outdoor conditions, rather than abruptly moving them from their cozy, sheltered existence into the cold, hard world.

Plants must be “hardened off” for a week or so by gradually exposing them to less-hospitable conditions for increasingly longer lengths of time each day. My plants progress from their windowsill nursery, to the unheated greenhouse in the daytime, to the unheated greenhouse 24 hours/day. I’ll start leaving the greenhouse door open, then setting them outside for the daylight hours. It’s best to put them out on a cloudy or partly cloudy day, as a full day of direct, hot sun can be hard on a plant. Plants can sunburn too! Eventually there will be a warm night and I’ll leave them outdoors. If frost is in the forecast, or a storm, I’ll bring them under shelter until it’s clear again. Eventually the plants will become more hardy, and spring will really be here, and around late May to early June I’ll be able to risk planting them out.

Into the Garden

This transplanting technique from pot to outdoor garden minimizes transplant shock and encourages strong root development.

Rather than digging a hole and planting the rootball at the bottom, as when re-potting, lie each tomato in its place horizontally on the outdoor garden bed, then bury it in soil — again, up to the top set of leaves. Be careful to support the stem, to avoid snapping it. Carefully pat down the dirt to ensure plant/soil contact, then water the whole plant thoroughly. The top of the tomato plant will eventually turn up toward the sun and grow into a surprisingly strong stem, supported by the amazing root system you’ve helped it develop.

It might seem easier to dig a trench and lie the plant in it, to keep your garden bed nice and flat, but if you do this you risk exposing the plant to the chillier soil underneath that sun-warmed top layer. Tomato plants may turn blue/purple-ish as a result — a sign of transplant shock. They will take longer to recover, which may affect the time or quality of harvest.

Have your own tomato-starting secrets to share? Tell us about it below…

Neophilia
Noun. A strong affinity for novelty. Neophiles (also known as “Neophiliacs”) adapt rapidly to changes and loathe tradition, repetition, and routines.

Here Comes the Sun

Sunlight is the first order of life – the energy that drives the life systems of our planet, from humans to plankton. So it follows that the ‘heart’ of your indoor garden is the grow light. After all, its purpose is to provide the incident energy required by your plants to grow and bloom: to synthesize the sun. The grow light is the motor of photosynthesis in the indoor garden, driving all other plant processes.

Today, the majority of indoor gardeners in North America use 1000 Watt High Pressure Sodium (HPS) lamps to light their plants and many growers still use magnetic ballasts. It may surprise you to learn that this technology has been around in more or less its current form for over 30 years. In other disciplines, most notably computing, a great deal has changed during this time. Can you imagine buying a personal computer today that even closely resembled that which was available thirty years ago? In 1980 the latest and greatest microcomputer boasted a measly 16kB of RAM (barely enough to store a ringtone these days) and a 5-inch CRT display. If you’re not abreast with the current state of computing technology, then consider this: a megabyte of storage would have set you back over $6,000 in 1980. Today, one hundred times this amount can be purchased for under a dollar. Things have moved on.

So what drove this huge amount of innovation? Essentially, nothing more than a heady mix of human ingenuity and rampant consumerism. That is, we all went crazy about computers and demanded more and more. In just a few decades they went from being arcane university research projects to being suffused into almost every part of our mainstream culture. Will the recent and dramatic rise in the popularity of indoor gardening serve as a similar catalyst for technological development in the field of indoor horticultural lighting? We certainly hope so.

New Paradigms of Lighting for Plants

If computers are measured in terms of processor speed and memory capacity, what is the equivalent set of metrics for the performance of a grow light? Okay, okay, obviously a grow light should make things grow. And the plants we want to grow have all evolved over millions of years to best exploit the solar energy generated by the Sun. So we don’t need a Ph.D. in Photobiology to assert that the Sun is the only benchmark we need when it comes to producing artificial light for plants.

That’s a point worth restating. We’re talking about light for plants here, not for humans. It’s very important that we de-personify both our plants and, for that matter, our grow lights. Lumens measure general light intensity for the human eye, not the photo-systems in the leaf. What we perceive as a single color is actually a combination of many different wavelengths of light.

How plants relate to light is more like hearing would be for humans: by frequency. Sunlight contains a ‘full spectrum’ of different frequencies. PAR light, nanometers, and other older references for light can’t be used as a reference for frequency; nanometers and frequencies are inversely related (backwards) to each other. Frequency means it’s more about the energy that plants really need, and nanometers is more about what’s best for people to understand.

The "Plant Sensitivity Curve" shows photosynthetic response to light at various wavelengths. (X axis = WAVELENGTH (nm); Y axis = "SENSITIVITY") Photo credit: Chameleon Grow Systems.

One of the primary reasons that HPS light was adopted by indoor gardeners is a NASA study produced over 20 years ago that basically stated: “Plants are efficient at using red light.” You have probably seen the spectral distribution charts on some HPS lamp packaging showing the peaks in spectral output. However, plants are efficient at using red light because, of all the colors in the spectrum that shine on the Earth from the Sun, red light has the least amount of energy. Photobiologists refer to this in terms of “electron volts per photon.” You can excite the cells of a solar panel with a violet light that has 3.1 electron volts per photon. But shining red light that has only 1.7 volts per photon on a solar panel is not sufficient to excite the cells. So, just because plants are efficient in using the low amounts of energy in the red parts of sunlight, it doesn’t necessarily mean that the best lighting for plants is high in the red parts of the spectrum. We don’t need to bombard our plants with red light. Plants require all the colors of the light spectrum as they utilize these different parts in different ways.

Another reason HPS light is used by indoor gardeners is to imitate the commercial greenhouse growers who use HPS for daylight supplementation. However, it’s important to note that, in greenhouses, HPS is used in addition to the blue light of natural daylight. It’s clearly a different ballgame to grow indoors using only artificial light, and we should treat it as such.

Who Turned Up The Heat?

So what’s an indoor gardener to do? We want to give our gardens lots of light – especially if we are growing light-loving varieties such as tomatoes and capsicums. HPS lamps output a lot of light, but in limited parts of the spectrum. They also produce a LOT of heat in the infrared part of the spectrum. And, as we all know, unless you’re growing indoors in Alaska, excessive heat is the nemesis of the indoor gardener. Surely there has to be a better way to grow indoors? Think of all those kilowatts of energy used to power grow lights, and all the kilowatts of energy used to power air conditioners, chillers and fans to remove the heat they generate! What technology exists to give our plants all the light they need indoors without creating other problems that require energy-intensive solutions? Do we need to improve current technology or go back to the drawing board? Do we need new lamps? New ballasts? New reflectors? New light movers? These are all very important questions.

Before we embark on our preview of alternative grow light technologies, please bear in mind that some of these technologies are further away from being stocked in your local grow store than others. Research and development is happening all the time, and this work is not confined to universities – real growers (albeit super enthusiastic hobbyists) are involved too. Right now, some of these technologies, for a variety of reasons, are less accessible than others. But things will change, if we drive that change. Remember, it was possible to buy a 1GB hard drive in 1980 – it was just the size of a refrigerator, weighed 550 pounds and cost $40,000! Today a hard drive 500 times that size will comfortably slip into your pocket … if there’s room! (It will only set you back $70.)

Now put yourself in the shoes of an IT enthusiast in the ‘80s. Are we at an equivalent point on the technology/accessibility curve for indoor garden lighting? If so, these are indeed exciting times! Okay, that’s quite enough preamble! Let’s take a look at the contenders …

Light – A Crash Course

The human eye is most sensitive to a yellowish green color. But what seems 'bright' to us is not what plants respond best to. Photo credit: Chameleon Grow Systems.

In one sense, light can be thought of as electromagnetic radiation, like radio waves, microwaves waves, X rays and gamma radiation. What we refer to as ‘visible light’ is simply the radiation that we can sense with our eyes. The average human eye will respond to wavelengths from about 380 to 750 nanometers. We perceive light as colors, with our maximum sensitivity at around 555 nm, in the green region of the optical spectrum. Light with a wavelength of 380-450 nm is perceived as violet. As the wavelengths become shorter it becomes ultraviolet (UV). At the other end of the visible light scale, wavelengths of 620-750 nm are perceived as red. As the wavelengths become longer (infrared) we perceive this electromagnetic radiation as heat, rather than light.

Light can also be conceived as a stream of light particles, called photons. One method to calculate the intensity of an artificial plant light source is to count the number of photons that hit a leaf per second. The unit for this calculation is “micromoles per second” (μmol/sec). Some growers reference the Photosynthetic Photon Flux (PPF) – just the photons that are between 400 and 700 nm. This is clearly a more relevant way of measuring light intensity for plants than, say, lumens, but it should still only be treated as an indicator. When all has been said and done, we’re trying to establish the quantity of usable light that hits the leaves of our plants.

Spectral Distribution

The distribution of energy in the lamp on the frequency spectrum is called the Spectral Distribution. The Sun has a full, continuous spectrum – and that’s what we’re aiming for too with our grow lights. The ideal grow light efficiently transforms electricity into the maximum amount of usable light energy (for the plants), with as little heat (infrared) as possible. Other factors to consider are lamp life and depreciation, and, of course, cost!

Inverse Square Law

Remember, if you double the distance between a leaf and your artificial light source, the amount of energy that hits the leaf is divided by FOUR. Stated another way, when you double the distance from the light source you lose 75% of the light energy from the light source. So when we talk about how much ‘usable light’ a grow light puts out, we need to consider environmental factors too – namely heat! Experienced indoor growers shoot for a temperature of around 80-82°F around the canopy of their plants in a CO2 enriched environment, slightly less for atmospheric CO2 levels. It’s important that we evaluate the potential of any grow light in the “real world,” and not just the isolated data of manufacturers’ technical specification charts.

Sulfur Plasma

Plasma International's Sulfur Plasma grow light. Photo credit: Clive Wing & Boris Lutterbach and Aad Baar.

Plasma International, a British/German company, has developed a grow light based on sulfur plasma technology. The lamp and magnetron unit is an electrode-less lamp that includes an evacuated quartz bulb partly backfilled with argon and with a little sulfur, plus a source of microwave power, a magnetron, for exciting a ball of plasma within the bulb. The lamps themselves are manufactured in Germany and can be powered by any 400W to 1400W Plasma Lighting System. The lamp produces almost no ultraviolet light and just a little infrared. It delivers a full and continuous spectrum (which means there are no troughs or missing/lacking color content). Full spectrum lighting is regarded as crucial for healthy plant development because it’s what plants have evolved for millions of years to exploit.

Wageningen University in the Netherlands has been using Plasma International’s Sulfur Plasma lamp to research simulating daylight in an indoor environment. Researchers had to shine the incredibly powerful light indirectly at cucumber cuttings through mirrors and filters. The tests, conducted in a climate-controlled room, showed that young cucumber plants grew much better then under HPS. Researchers believe this is due to the color of the light and its ability to influence the shape of the plant. At the right light color, the young plant captures light energy far more easily.

The cucumber plants grew more than 60% faster than those grown under HPS, and more than 120% better than those grown under compact fluorescents! There was also a marked increase in branching and larger leaves. The first results (released September 2009) also showed that the specially-created artificial sunlight spectrum made the young cucumber plants 64% heavier than those grown under HPS (SON-T) light, at equal light strength.

Plasma International’s lamp draws 1300W from the mains and delivers 1000W to the bulb. It is dimmable down to between 10-40% depending on which bulb is being used. The moving parts inside the lamp are guaranteed for 100,000 hours of use – this movement, the manufacturers claim, gives greater control over the plasmoid. They also claim that they can quite easily alter the mix of the bulb and adjust the spectral output to specific applications. To date, Plasma International has developed one lamp for vegetative growth and another for flowering. The lamps produce less than half the infrared heat per watt compared to HPS or Metal Halide.

The lamp comes as two boxes. Each box is 9” x 6.6” x 6.6” in size. One box contains the plasma-i-tron and the other is the power supply. The lamp can easily cover the same area as a 1000W HPS but, because of the reduced heat, it could be positioned closer to plants.

More information: www.plasma-i.com
Time to market: 1-2 years.
Cost: Currently only available for research purposes. Expect to pay upwards of $3,500 per unit.

Light Emitting Plasma – LIFI

Luxim's lightweight Light Emitting Plasma Emitter.

Luxim Corporation in California has developed a solid state light emitting plasma – it uses metal halides and argon, not sulfur. It uses no electrodes and draws 266 watts. Their latest model, announced in February 2010, is the LIFI-STA-41-02. Luxim only produces the light unit. It is up to companies further down the ‘technological food chain’ to develop specialized appliances for their specific market, such as TVs, theatrical lighting, healthcare, horticulture, etc. Crucially, the LIFI Plasma light was NOT invented to grow plants. The spectrum is still lacking a lot of red.

LUXIM is researching how to use different metal halides in the plasma cell in order to create a better spectrum for plant growth. Until they, or somebody else, figures this out, various companies in Europe and North America are experimenting with LEDs in an effort to correct the spectrum. However, whether this is actually possible or not remains a bone of considerable contention. One such example is Chameleon™ Grow Systems in Florida. They have developed the Solar Genesis VI (due for release later this year) which houses two LIFI plasma units and banks of high output LEDs. Infrared (IR) radiation from the light is minimal.

The Solar Genesis VI spectral output compared with an HPS, overlaid on plant light sensitivity. Photo credit: Chameleon Grow Systems.

The internal ballast has 91-93% conversion efficiency and the lamp life is rated at an incredible 50,000 hours (11.5 years) with no replacement every 9-12 months necessary.

The Solar Genesis VI supplements two Luxim 266 watt LEP units with four banks of high power LEDs. Photo credit: Chameleon Grow Systems.

Tech Stats: LIFI-STA-41-01
Emitter Length: 72.9 mm
Emitter Diameter: 116 mm
Driver Unit L × W × H: 193 × 85 × 32 mm
Rated Average Life: 30,000 hours
Total Initial Lumens: 15,000 lumens
Typical Turn-on time: 30 seconds
CCT: 5800 K
CRI: 94
Dimming Range: 20-100%
Nominal AC Power @ 277v 266 watts

More information: www.luxim.com www.chameleongrowsystems.com
Time to market: 3-6 months
Cost: $7,000 per unit for Solar Genesis VI

Other Technologies

Phillips HPS 400V

Lumatek's new ballast will enable growers to run highly efficient 400V lamps on 230V power.

Lumatek is in the process of developing a new 400V professional ballast that drives the professional Phillips HPS 400V lamp, but runs on normal 230V. Gavita, a leading European horticultural lighting company, has teamed up with Lumatek to develop and bring their products to the indoor gardening market. Industry insiders concur that this allegiance is great news for growers!

The 400V bulb, which is more efficient, performs more consistently and lasts longer – and it has an enhanced spectrum. Even better: it was built specifically to run on electronic ballasts.

Time to market: 3-6 months
Cost: To be announced
More information: http://tinyurl.com/yjzx2dk (pdf)

SunPulse® Pulse Start Metal Halide

SunPulse® bulbs were specifically designed to produce the true photochemical reactions plants need to make the maximum amount of photosynthesis and produce the most chlorophyll. This is a very important point. SunPulse® bulbs were made for plants. They were designed by Gerald Garrison – and if that name sounds familiar, you may remember he was featured on the cover of Urban Garden Magazine 003 in relation to his indoor food production facilities in February 2009.

The original SunPulse® digital bulbs, the first digital bulbs to ever be introduced, are made in four unique Kelvin colors: 3k, 4k, 6.4k and 10k. The lamps’ wattages range from 100 to 1000.

SunPulse Pulse Start Metal Halide Lamps were designed for specifically for plant growth.

Central to their lighting model is a photosynthesis delivery system which houses and rotates multiple lamps (of different Kelvin temperatures) over the plants, to provide full spectrum lighting. A lighting schedule is located on every bulb box which outlines when to use each particular bulb, as well as suggestions for those who aren’t budgeted for four bulbs per fixture.

SunPulse’s 1000w Commercial Grade bulbs were originally designed exclusively for commercial food production facilities, but are now being made available to growers everywhere for the first time. The Commercial Grade bulbs come in three proprietary colors: 2.8k (fruiting/flowering), 5.7k (full spectrum) and 10k (ripening). Commercial greenhouses around the world are already enjoying the benefits of the greater efficiencies and color rendering made possible by this series of bulbs. The Commercial Grade lamps’ high-temperature tolerances, rugged design and top quality components are the perfect choice for full-scale production facilities and now are available for smaller producers as well.

Time to market: Available now.
Cost: 1600W 4 x 400W (3K, 4K, 6.4K and 10K) Spinning Light Complete System – $1,950
More information: www.sunpulselamps.com and www.lifelighttec.com

Want to know more about these or any other horticultural lighting technology? Fire your questions at will by posting a comment below!

Novice growers are notoriously wary about pruning. Maybe it’s because it seems wrong to hack away at a perfectly healthy plant – or perhaps pruning is mistakenly associated with pure aesthetics? Whatever the reason, pruning is arguably more important indoors than anywhere else. So we asked Kevin Anderson, a hobby grower in British Columbia, Canada, to share his wisdom on the art of manipulating light-loving plants indoors.

WORDS: Kevin Anderson

Okay, let’s start with a simple fact that’s worth repeating. Growing indoors is different to growing plants outdoors. The biggest difference is the light source. Light, as we know, is the ‘motor’ that drives the whole growth and bloom process. The Sun provides all the light our plants need when growing outdoors. But indoor growers typically rely on high intensity discharge (HID) grow lights to provide the input energy required for photosynthesis.

But that’s just the beginning of the story. The differences between the properties of the Sun and your 1000W High Pressure Sodium grow light are so numerous that comparisons seem ludicrous. After all, the Sun is 93 million miles away from your plants whereas your grow lights are just a few feet! The intensity of the light from your grow lamps diminishes exponentially the further your plants are positioned away, whereas a few extra inches or feet doesn’t make any difference to the energy received from the Sun. Additionally, if any part of your plant is too close to your grow lamps they will quickly become heat stressed / burnt.

Light intensity decreases exponentially with a linear increase in distance from the grow light.

So if you want to grow light-loving plants indoors, you need to address this key question: how do you get sufficient light energy to your plants without causing them heat stress? Most indoor gardeners hang their grow lights above their plants, using a reflector to direct light down towards the canopy. The inverse square law tells us that if you double the distance between your plants and your grow light, the intensity of the light hitting the plant is quartered.

The ‘sweet zone’ is the ‘not too near, not too far’ space under the grow lamp that receives the most light energy without being so close to the lamp that the heat from the lamp interferes with the plant’s health and metabolism. The aim of the indoor gardening game is to shape and position your plants so that as many growth tips / fruiting sites as possible are basking in the ‘sweet zone.’

The sweet zone’s distance from the lamp depends on the size of bulb you are using, the reflector (if used) and whether your lamps are stationary or mobile. Lamps on a rail or rotational device can be placed closer to plants because, as they are moving, there is less danger of hot spots developing. In the case of stationary grow lights and in the absence of a light meter, I hold the back of my hand under the light and move it away until it feels comfortable and doesn’t continually get warmer: this is what I call the ‘sweet zone.’ Despite my less-than scientific approach, there is nothing esoteric or mystical about this. You need to get your grow lights as close as possible to your plants without frazzling or stressing them. Period. Experience counts for a lot here! So your mission, as an indoor grower, is to manipulate your plants so that as many of these flower / fruit sites as possible end up in the ‘sweet zone’ so they can ripen and mature to their full potential, basking in high light levels at the optimum temperature.

Now we have the basis of an understanding of why pruning and manipulation techniques like topping and bending could be so important to indoor gardeners. Put simply, it’s all about getting as much of your plants into that ‘sweet zone’ as possible!

Whenever a plant grows (roots, stems, leaves, flowers, fruits) it takes ENERGY. The rate of a plant’s development is limited by the amount of light (ENERGY) it receives. This energy is distributed throughout the plant in order to grow and bloom. The aim of pruning is to focus this energy to where it’s most needed – the fruiting sites in the ‘sweet zone.’

KNOW THY PLANT

What happens if you don’t prune, top or bend? What’s wrong with just letting your plants do their thing? Left up to the plant, whatever incident energy is received from your grow lights will be focused where auxins (plant hormones that regulate growth) are most present: i.e. in the main/ central leader (the trunk). Auxins will always accumulate at the top of the plant and wherever they collect grows more … keeping the top of the plant … at the top!

Conceptual illustration of a cutting left to grow into its natural form under a grow light.

In the illustration above, the top of the plant is too close to the grow lamp and will quickly start to suffer from heat stress or burning. This will stunt the growth just at the point where all the action should be! What a tragedy! Meanwhile the lower branches of the plant are not receiving much light. We can raise the grow light, of course, but this means that the lower parts of the plant are forced to suffer even lower light levels, just to keep the tip (a tiny percentage of the plant’s overall biomass) out of trouble.

Houston, we have a problem! And the problem is the form of the plant. Tall and triangular, like a Christmas tree, may suit the Sun, but it doesn’t suit a grow light hung from above! The plant doesn’t know that it’s in a totally different scenario to outdoors – so it’s just doing what millions of years of evolution have programmed it to do. It ‘thinks’ it’s growing under the sun, where light intensity up and down the plant is far more uniform. Topping, bending, and low stress training (LST) are all manipulation strategies that the indoor gardener can employ to engineer the shape of their plants so that they can best exploit these precious grow light photons. The aim of pruning and bending is to redistribute auxins through several shoots, rather than just the top leader, thereby encouraging the plant to produce a number of equally dominant branches instead of just one ‘uber top.’

Many indoor growers use pruning and other manipulation techniques to engineer squatter plants with wider canopies – like a candelabra. A wider, even canopy allows for more growth tips and fruiting sites to bask in optimum light levels as opposed to a plant that is allowed to grow a narrow peak.

TOPPING

Topping refers to the practice of removing the top of a plant. This promotes the growth of the satellite growth tips and a wider canopy. I use a clean, super-sharp scalpel to top my plants. If topping multiple plants, clean your chosen pruning tool between cuts with some rubbing alcohol. It sounds a bit anal, but you wouldn’t want a surgeon to use the same instruments on you that they’d used to operate on the previous patient, would you? Different growers top their plants at different stages. I’ve topped my plants when very small (e.g. at the fourth internode) and when they are a foot or more high. Keep in mind that the more plant matter you remove, the more you stress the plant. Generally speaking, plants take a few days to recover from topping and resume previous growth rates.

‘Pinching out’ is another term you may have come across. This refers to the act of removing a new growth tip only, rather than any stem. I’ve enjoyed my highest levels of success by pinching out the lead growth tip a few days before enducing flowering. This is just enough time for the plant to overcome the stress and redistribute the auxins. The plant will then begin to branch out, resulting in a more even canopy with more tops.

The same plant after being topped at the eighth internode. Compared with the un-topped plant, it has many more fruit / flower sites in the sweet zone with no extremities erring too close to the hot bulb.

Note: topping is not suited to all plant varieties or cultivars. If you are unsure how your plants will respond, try it on some cuttings but not on others and compare results. Don’t just compare yield – compare fruit quality and modal (rather than median) fruit / flower size too!

THE ‘CLEAN-UP’

The same topped plant, but now with lower branches removed to focus fruit development in the ‘sweet zone.’

The ‘clean up,’ as I like to call it, is another type of pruning that is widely practiced by indoor gardeners. Once again, it’s all about focusing the plant’s energy into fewer, larger, higher quality fruits. If left un-cleaned, a light loving plant grown indoors will generally produce many small, low quality fruits and flowers, especially on the lower branches. This is because of reasons already stated: the light from a HID bulb loses intensity and does not penetrate the dense canopy above. But remember, these lower yielding regions will still draw from the plant’s finite energy reserves and often the fruits take longer to ripen. Through a timely removal of the lower down, shaded growth tips and branches, the plant has less potential fruiting sites over which to spread its energy. It still has the same amount of energy (as long as not too much plant matter was removed in pruning), and there is still a dense canopy to bask in the full light; however, this energy is now focused on a lower number of fruiting sites resulting in even larger, higher quality fruits. Pruning off the bottom of the plants and removing crowded branches has the additional benefit of creating better air-flow through and under the plants, helping to prevent conditions which promote molds.

CLEAN-UP AFTER STRETCHING

Many types of plants will experience a growth spurt during the transition between vegetative growth and flowering (generative) growth. I think the best time for the clean up is immediately after this initial ‘stretch’ (but before the plant has shown much sign of fruiting). If too much is pruned off too soon, the plant will stretch even more and become somewhat leggy. If you clean up too late, you will be removing green matter that the plant has already invested a lot of energy into, some of which will be small fruits or flowers. The later you prune into the flowering stage, the more the plant is focusing its energy on generative growth instead of vegetative. A good rule of thumb is to “clean up” the plant in the second week of flowering just as the first small signs of fruit appear and after the plant has stretched a little.

HOW MUCH IS TOO MUCH?

There is a fine line between pruning off too much and ending up with a very sparse canopy and a loss in yield, and leaving too much on and lowering the size and quality of the fruits. This takes some experience. There are many variables to consider: plant variety, plant density, veg times, etc. Less pruning is required for plants that have more space; more pruning is necessary for denser gardens.

Aim for an even canopy with an abundance of fruiting sites basking in the sweet zone!

Generally, I tend to prune off all branches lower than halfway up the plant. As the plants start to flower you should be able to crouch down and peer right through your garden, underneath the dense canopy. Prune off fruiting sites 2/3 to 3/4 of the way up the plant on the less dominant branches, and about halfway up the plant on the dominant branches so there is a slightly sparse canopy. This may seem a little too much at the time, but the plant is still going to grow quite significantly and will fill in a lot before it finishes stretching.

Do you agree with Kevin’s pruning strategies? Tell us what you think below!

The winter time is when indoor gardening shines. Bright lights, CO2, and enclosed spaces all make for a potentially hot environment for any plant. Some plants thrive in hot environments. Most do not. Winter is when the outdoor ambient temperatures help reduce, depending on your location, the effect of those heat factors.

Winter is one season in four. For the rest of the seasons, you may need to cool your environment. If you don’t, you risk lower yields and heat stressing your plants. Or, you must limit yourself to hot-thriving species.

Two kinds of cooling exist today for grow rooms: ambient air cooling and liquid water cooling. Ambient air cooling requires an air conditioner and ventilation to exhaust the hot air from the grow room. Water cooling requires the same and focuses on providing a cold solution near the heat source (typically, the grow light). Where air cooling pushes cold air to every aspect of the grow area, water cooling targets just the heat-producing areas of your grow area (typically, your light and reflector).

Let’s talk about Hydro Innovations’ ChillKing & Ice Box. The ChillKing is Hydro Innovation’s liquid chiller solution. I received both the 1/2 HP ChillKing and Ice Box at the beginning of the summer growing season.

Ideal temps for indoor gardening are an ambient 72-75 degrees Fahrenheit. Every grow room maintains different ambient temperatures. My grow room, in the summer, runs as hot as 100 degrees Fahrenheit. Talk about plant heat stress.

That was, until I installed a 1/2 HP ChillKing and a 6″ IceBox from Hydro Innovations.

Hydro Innovations offers their ChillKing in 1/2 HP through industrial-engorging 10 HP. The IceBox is available in 6″ ducting and 8″ ducting sizes.

The ChillKing is a essentially an air conditioner with liquid cooling plumbing for the water path. On the side of the ChillKing is an electronic temperature control which will power on the unit—thus cooling—when the water flowing through its input/output flows in above the temperature set by you.

The 1/2 ChillKing can either be mounted through a wall or window sill (as with traditional window A/C units). I used an 1800 gph submersible pump and 35 gal water reservoir for my cooling. With the ChillKing, I believe that you could use an even smaller water reservoir (25 gals even) for chilling–depending on your lighting setup. The cold water response from the ChillKing is near flash-instant, from hot water to cold.

This unit is completely different from the cheap plastic units currently available. The ChillKing is built like a brick s***house. Not a single cheap component. Metal components throughout and metal hose connectors.

My only suggestion for improvement for the ChillKing would be at the hose-connections.  Instead of screw-on, fixed hose connectors on the unit, I would like to see garden-hose free-spinning connectors or even quick-connectors.  Without this, once you connect your water lines, you may be twisting the entire hose to manipulate it onto its receiving connectors (water reservoir connection, pump connection, IceBox or Fresca Del Sol connections, etc…).  Depending on your setup, this can be a pain.

Add the IceBox.

With a 6″ IceBox and a 440CFM 6″ Can-Fan fan connected to my 600W light and reflector, the pair worked wonderfully! The temperature dropped dramatically from summer months scorching my grow chamber. My grow chamber dropped from 100 degrees F day / 85 degrees F night to 74 F day / 70 F night. Previous to installing this, I had to focus on temperature resilient and heat-thriving plants. After implementing this setup, the plant kingdom is my oyster and I will grow what I want.

However, the ChillKing & 6″ IceBox could not and cannot drop my grow chamber temperature below 68 degrees even with the light off (flowering darkness). If you’re a grower who needs to drop their lights-off flowering below that temperature (some growers would like to hit around 60 degrees F), I would recommend stepping up to an 8″ reflector and the 8″ IceBox for more CFM air flow.

Worm-gear clamps cinching the connections to the IceBox.

My only improvement suggestion for the IceBox is the same as for the ChillKing—quick connect connectors. I had to wrap tape around the input/output connectors and cinch the connections water-tight with small worm-gear clamps. Especially useful would be quick-connections which would also retain the water in the hose when removed from the IceBox. Otherwise, moving/reconfiguring the IceBox will lead to a watery mess.

The ChillKing and IceBox allowed me to increase my yields, avoid heat stress, AND expand the types of plants which I can grow. I will not return to a chiller-free setup.

In case you missed them, Hydro Innovations offered complete setup deals (chiller, hoses, IceBox, water reservoirs, and and everything you would need) across this past summer. Look for their current pricing and any promotions at: http://www.icehousedistribution.com/.

NOTE: please read Part 2 for the update, which corrects the set-up mistakes made here.

Please note: blog posts are the opinions of independent growers, and do not necessarily reflect the opinions of Urban Garden Magazine or its affiliates.

Everest shares some time-honored heuristics to help beginner growers increase the productivity of their indoor gardens.

1.) Reduce Your Concentration!

Hydroponic growers adjust the pH of their nutrient solution to around 5.8 to 6.2 – this provides the best accessibility to the widest range of nutritional elements.  pH adjuster products are sold in grow stores in concentrated liquid (sometimes powder) form.  However, some growers get lazy and add this stuff neat (undiluted) to their nutrient solution.  This causes nutritional elements to precipitate out of the solution and therefore become unavailable to your plants.  To avoid this, make up a dilute solution of your pH adjusters – 1 part pH adjuster to 100 parts water – and use this instead.  The weakened concentration of your pH up or down will enable you to safely adjust the pH of your nutrient solution without damaging your nutrients!

2.) So Near, So Far …

More light = more yield … but only to a point!  In fact, grow lights can represent a mixed blessing for the indoor gardener.  Sure, they provide the all-important light photons essential for photosynthesis – your plants ain’t growing without them!  But these same lamps also generate a lot of radiant heat!    If your plants grow too close to your lamps they will become too hot and shut down (stop photosynthesizing).  In extreme cases they will scorch and burn and the growth tips will die.  This causes untold stress to your plants and drastically reduces your yields.

On the other hand some growers are overly cautious and raise their grow lights too high, causing their plants to stretch in search of more lumens.  The ongoing aim of every indoor gardener is to get as many growth tips in the “sweet spot” as possible.  This is the area where your plants are just at a safe distance away from your bulbs and receiving maximum light intensity.

Different growers combat this problem in different ways.  All growers should try to move the air in between the tops of their plants and the lamp using an oscillating fan.  Some growers also air-cool or water-cool their grow lights while some put their lights on a mover or spinner.

As well as a light meter, use a thermometer with a remote temperature probe to measure the heat at the tops of your plants.  For many popular indoor crops, the magic number is 82°F (28°C).  What’s the temperature reading at the top of your plants?

3.) Brrrrr!  Using Cold Tap Water!

First off, tap water can contain chlorine and chloramines plus high levels of other minerals (often not in a form that is useful to your plants) and other impurities.  You should always feed your plants with the best quality water you can.  Many professional growers and keen hobbyists take control over their water quality by investing in a water softener and reverse-osmosis water purifier.  Also, you should always make sure that the temperature of your nutrient solution is around 65 – 68°F (18 – 20°C) before feeding it to your plants.  Cold water shocks your plants’ roots and warm water contains drastically lower levels of dissolved oxygen.  If your indoor garden is suffering from high temperatures, using a slightly cooler nutrient solution can help your plants get through until you manage to correct your environment.

4.) Lights++ Environment–

So, you’ve managed to dial in your indoor growing environment with two, three or four lights and you’re growing healthy, happy plants and enjoying regular crops of your favorite veggies all year round.  Great, but don’t make the mistake of thinking you can expand by simply adding more lights!   You need to also consider how this will effect your growing environment.  Firstly, more plants will mean more transpiration, and a need for more CO2.  More lights equals more heat to get rid of.  So if you are thinking of adding more grow lights, make sure you budget for increased air transfer too – you’ll definitely need it!

5.) Unruly Plants

A crucial skill that every indoor gardener needs to learn is how to shape and train their plants so that they make the most of any artificial light source.  You need to let your plants know who’s boss.  Do not grow your plants too large.  Small to medium sized specimens are the way forward for most indoor growers.  Remember, your plants receive exponentially less light the further they are from the lamp.  As most gardeners light their plants from above, a common goal for many indoor growers is for shorter, squatter plants with wide canopies.  Think of a candelabra.  Pruning out the leading growth tip will encourage many types of plants to adopt this formation.

TIP:  If you are growing plants that are sensitive to photoperiod bear in mind that they will not respond immediately when you change your light cycle to induce flowering.  Growers of many plant varieties are often stunned by the amount their plants bolt (or stretch) after changing the day length simulated by their grow lights.  Err on the side of ‘small’ when deciding when to switch your plants from vegetative to flowering mode!

6.) Grow Like A Gardener, Not a Robot

So you think you’ve got your nutrient recipe down and now it’s just a question of making it happen.  But the best growers are always in a state of flux.  They are observing their plants on a daily basis, getting in among them, looking for signs of under / over fertilizing and adjusting their nutrient regimen accordingly.

This is especially important if you are making any chance, whatsoever, to your growing environment.  Improved air exchange or CO2 levels in your indoor garden will cause your plants to grow more vigorously.  The saavy grower observes and recognizes this and increases the strength of his nutrient solution accordingly.

Conversely, if the ambient temperature inside your indoor garden rises above optimum levels (e.g. during the summer months) your plants will inevitably use more water.  You should therefore decrease the strength of your nutrient solution.

7.) Stale Food

Re-circulating your nutrient solution?  Great – you’ll save on precious water resources, not to mention expensive nutrients and additives!  But ask yourself – how often do you really drain your reservoir, then rinse, and replenish with a fresh batch?  Once every week?  Once every two weeks?  Or once every … when you can be bothered?  Younger plants will tolerate less frequent nutrient solution changes than more mature plants.  But if you’re really going to turn on the charm, the time for super frequent nutrient solution changes is during flowering and fruiting.  This is when your plants’ nutrient requirements are at their highest and will benefit most from regular nutrient solution changes.

8.) Poor Propagation

Care early on pays massive dividends later.  Be especially patient and watchful during the propagation stage.  Give your plants time to establish healthy root systems before rushing them into a hydroponics system and flowering them off.  Ensure humidity levels are kept fairly high at 60-80%, especially early on.  This reduces stress on the young plant which, in turn, allows it to focus on that all-important root system.

A plant that has been “hardened off” for five or six days under a fluorescent veg lamp, for instance, still needs to be introduced to a 1000W metal halide with care.  Raise the metal halide 3-4 foot above the plants until you see the first signs of growth.  Break those babies in slowly.  What is often diagnosed as “transplant shock” is often more due to the shock of an increase in light intensity.

9.) Lack of Oxygen

Dissolved oxygen in your nutrient solution is so important we can’t harp on about it enough.  Oxygen in your nutrients promotes root health and speeds up your plants’ metabolism meaning it can grow faster and bloom copiously!  Lack of oxygen in your nutrients, on the other hand, invites all sorts of problems, the leader of the pack being pythium which can destroy your crop in a matter of days.  You can increase levels of dissolved oxygen in your nutrient solution by bubbling air into it – the smaller the bubbles, the better!

10.) Don’t Be a Dirty Sanchez

What’s that carpet still doing in your indoor garden?  Is that decomposing plant matter in the corner over there?  Still not got rid of that bag of old root balls from last crop?  Get a grip on your garden!  Clean as you go.  Keep it as spotless as possible.  Filter all air vents.  Think of your indoor garden as a laboratory and you won’t go far wrong.  The cleaner your growing environment, the fewer viruses your plants have to fight; the more energy your plants can put into their primary mission – growing and blooming!  Cleaning sounds boring, and it is.  But how boring is 10% more yield?  Nuff said.

So is it any wonder that our ears pricked up when we heard that there might be a new super weapon for us indoor gardeners to use in our fight against pests and molds?  What might this be?  UV-C?  Are we serious?

Ok, so UV-C’s germicidal properties have been known since the 1930s but it’s remained an unfamiliar technology to most indoor gardeners.  And now with new UV-C T5 lamps becoming commercially available, could UV-C technology be used safely within our indoor gardens as a room sterilization tool, part of an ongoing preventative routine, or even as a reactive treatment for bugs and molds on the plants themselves?

If you put a UV-C lamp anywhere near your plants and leave it on for a few hours, the leaves will soon appear to be damaged / scorched.  Again, I repeat, UV-C kills stuff!  So what place, you may well ask, does UV-C light have in an indoor garden?  We don’t want to kill our plants!  We want them to grow and thrive!  I understand your concerns, Urban Gardeners, but please give me time!  Despite being a relatively old technology, this particular application of UV-C is right on the cutting edge.  I’ve also got a very scary looking lawyer stood right behind me advising me to type these warnings in big, bold font.

The Basics

Okay, for those of you who aren’t so familiar with UV, let alone UV-C, here’s a quick run through the basics.  Ultraviolet light (UV) occurs naturally from the Sun.  UV has a wavelength that is just outside of our visible range.  We tend to refer to light that is visible to our naked eye as various “colors.”  The lowest wavelength color we can see is “violet”, hence the name for light with a wavelength just lower than this is “ultraviolet.”

Now it turns out that the term “UV” refers to a relatively broad spectrum of light – anything from 100 nanometers to 400.  So UV has been further divided into UV-A, UV-B, UV-C and UV-V.  The part we are interested here is UV-C.  It’s the section of UV between 185 and 280 nanometers – also known as “short wave ultraviolet radiation”. UV-C rays have the highest energy and are arguably the most dangerous part of UV light.  (Although some would counter that UV-B is more dangerous as it causes skin cancer.)  Solar radiation in the UV-C range is absorbed almost entirely by the atmosphere.  Artificial UV-C lamps have been shown to be super effective in the laboratory at destroying bacteria, mold, viruses and certain plant pests as well as other biological contaminants in air, liquids, or on solid surfaces.

UV in Nature

UV is Mother Nature’s blanket method of controlling pests and pathogenic microorganisms.  Crops grown in greenhouses (which filter out UV) and indoors under high pressure sodium lights (which emit virtually no UV) have tended to be more susceptible to pests and pathogenic fungi.  Higher humidity levels inside greenhouses and indoor gardens can also promote pathogenic fungi such as Phytophthora and Botrytis – serious pathogen families which can decimate crops.  And until now most growers have resorted to using expensive fungicides to combat these problems.  However, there is an increasing groundswell of public opinion against the use of these products, especially when used on crops intended for human consumption.

UV-C destroys a whole host of undesirables – from viruses, bacteria, mold, and mildew to plant pests like spider mites. UV-C rays are able to penetrate the outer membrane of microbes (e.g. algae, bacteria, mold or viruses) and stop them from reproducing.  The same is true of many plant pests (and their eggs) – the smaller the plant pest, the more susceptible they are to UV-C.  The specific wavelength of 253.7 nanometers is known to break the DNA of pathogens and smaller plant pests so that they are unable to reproduce.

But isn’t UV-C damaging to plant tissues too?  The short answer is yes!  But the same is true of Hydrogen Peroxide, Nitrogen, Phosphorus and Potassium when applied at levels that are too high!  The key question is:

Can precise doses of UV-C be used to treat plants directly in order to eradicate or control pathogens and plant pests without doing harm to the plants themselves?

If so, the net effect of UV-C treatment could be fewer pests and increased yields – because if your plants aren’t using energy fighting off pests and pathogens then they can put that energy back into growth and bloom.

Intellectual Property

In May 2007, two Dutch inventors, Arne Aiking and Frank Verheijen, were granted an International Patent on a method of treating live plants and mushrooms against pathogens and pests with UV-C light.  (International Patent Number: WO 2007/049962 A1.)  In the past UV-C had only been used to sterilize things like air and water.  Typically the germicidal effects of UV-C were achieved through the heuristic of “overkill”.  Use triple the amount of UV-C you think you need and you will definitely kill whatever it is you want to kill.  The water or air still remains perfectly intact after sterilization.  The difference, of course, with proposing to use UV-C to fight pathogens and pests on living plants is that you shouldn’t use any more than is necessary, otherwise there is a risk to health of the plant.

While the general method of using UV-C to kill pests and molds is now public knowledge through the World Intellectual Property Organization, the owners of this and associated intellectual property are keeping the details very close to their chests.  For instance, in the aforementioned patent, the application of UV-C is only broadly described:

“It has been found that amounts of UV-C light between 0.0025 and 0.15 J/cm2 during a period of 24 hours enables not to induce any, or at least not to induce plant tissue damage which has a negative effect on growth and yield of the plants while still having an anti-pathogenic effect, i.e. controlling pathogen growth.”

What does that mean in plain English?

Aiking and Verheijen's UV-C lamp would travel up and down water heating pipes like these in between the plants.

Well, it’s probably a good idea to look at the practicalities. Aiking and Verheijen’s invention is a mobile UV-C lamp that travels up and down the water heating pipes you commonly sees in commercial greenhouses.  This lamp periodically travels through the crop, dosing the plants either side with UV-C light.

How much UV-C light?  Well, again, specifics like these appear to be pretty closely guarded secrets right now. The emission or light intensity of a UV-C germicidal light bulb is usually expressed in a term called “microwatts per square centimeter” (μw/cm2) not J/cm2 (Joules per square centimeter.)  Aiking and Verheijen appear to be suggesting a range of between 2,500 and 150,000 microwatts of UV-C energy over a given 24 hour period.

But then the plot thickens when the patent describes the UV-C lamps to be used in the invention:

“UV-C lamp intensity of between 2 and 100 Watts with an effective exposure period of between one second and one minute and a proximity to the pathogen growth of between 2 cm and 200 cm.”

Hang on a second.  That’s quite a range of variables there!  Let’s just break those down:

If we take the lower end first:  We can safely estimate that a 2 Watt UV-C lamp will output approximately 1000 microwatts of energy over a square centimeter, in one second, from a distance of two centimeters away.  Remember, the inverse square law applies to all artificial lighting sources.  At 150 cm it’s less than 1 microwatt.  At 200 cm, it’s barely anything at all.

A 100 Watt UV-C lamp, on the other hand, will output approximately 14,000 microwatts of energy over the same area, in one second, from a distance of two centimeters away.  If we leave it there for one minute (the upper limit of the duration range specified in the patent) we have to multiply that figure by 60!  840,000 microwatts!

I guess, if we’re to make any modicum of sense of this huge range of numbers, we need some data on how much UV-C light is required to effectively kill various things.

For instance, tests have shown that powdery mildew is killed when given a dose of 1720 microwatts of UV-C per square centimeter. So, if I took the aforementioned 100 Watt UV-C lamp and positioned it two centimeters away from the mildew, I would need to switch on the UV-C lamp for just 1/10 of a second to kill it.  This is calculated by taking the effective dose rate (1720) and dividing it by the amount of microwatts reaching the target (14,000).  At ten centimeters away only about 3,600 microwatts of UV-C is delivered to the target, so about half a second’s exposure is needed.

Spider mites could possibly also be effectively treated with UV-C but with amounts that are hundreds of times more compared to something like powdery mildew.  Lower doses of UV-C may be able to control the increase of this bug, but it would be difficult to kill off large populations that have already established themselves.

As for as the effect of UV-C on plant tissue, another patent indicates that if the UV-C dose is under 200,000 microwatts, leaf damage was not observed.  This appears to be in the same region as the limits proposed by Aiking and Verheijen, however, at this point, these shouldn’t be treated as firm numbers.  Certainly the safest way to use UV-C on plants appears to be regular, smaller doses rather than a single, large hit.

POSSIBLE APPLICATIONS

Room Sterilization Between Crops

UV-C lamps could be used for sterilization of small growth chambers before plants are introduced.  Of course, the grower should still clean the chamber in the regular way using a mild bleach solution and a sponge, but then it would be quite feasible, as an added precaution, to expose the growth chamber to UV-C light to deactivate any residual pathogens, insects or eggs that might still be lurking in the growth chamber.

What about a UV-C Sterilization Chamber?

One possible application of UV-C could be to create a ‘cleaning chamber’.

A small ‘clone-box’ sized light-proof grow tent could be fitted with  UV-C lamps hanging from the top, and banks of UV-C lamps fixed on each side panel of the grow tent.  Plants could be placed inside the chamber when the UV-C lamps are switched off, the grow tent is zipped up and light-proofed, and the UV-C lamps are switched on for a precise amount of time to kill / control the pest or pathogen while remaining under the range where plant tissue is damaged.  Remember, when it comes to UV, plant tissue is hardier than your skin!

Certainly, small plants would present less of a challenge than larger ones, simply because there are fewer places to hide.  A key consideration when using UV-C for pest and pathogen control is crop density, which makes a dedicated UV-C chamber a more attractive possibility.  Of course, plants would have to be mobile (e.g. grown in pots) and the UV-C lamps would still need to be arrayed in such a way that there was a sufficient spread of UV-C energy hitting all parts of the plant.  Remember, the inverse-square law of indoor lighting intensity also applies to the germicidal properties of UV-C in that they decrease exponentially the further an object is from the artificial UV-C source.

A dedicated UV-C grow tent would also be very useful to anybody wishing to research the levels of UV-C exposure that healthy plants can tolerate without affecting growth and yield through comparison with a control plant that does not receive any UV-C.  It should also be noted that younger plant tissue can tolerate less UV-C without sustaining visible damage.

UV-C Within the Indoor Garden?

UV-C applied every day for short periods of time could keep some pests and pathogens under control, and help to sterilize the surrounding air.

For UV-C to be used within an indoor garden, banks of UV-C lights would need to be arrayed so that all plants were being hit fairly evenly from top to bottom with UV-C energy.  This would obviously involve placing UV-C lights in between plants at even intervals.  The UV-C lamps would then be switched on for a fixed amount of time each day (we’re talking seconds or minutes depending on the wattage of the UV-C lamps.)

An important note:  the target bug or pathogen must be hit directly with the UV-C rays in order to be affected.  If it is shaded / protected by a leaf, for example, the UV-C will not be effective.  UV-C will not penetrate through leaves so it would be really important to get the UV-C to the underside of the leaves too.  This could be achieved by lower lamp placement at the level of the soil or growth media.  If there is also air movement, the leaves of the plants will move and more leaf surface will be exposed to the UV-C.

If UV-C is going to be used in an indoor garden it would be advisable to incorporate some sort of “kill switch” that automatically turned off the UV-C lamps if the grower inadvertently entered the room while the UV-C lamps were operating.  Just to reiterate (again!) …. YOU DO NOT WANT TO BE ANYWHERE NEAR A UV-C LAMP FOR ANY AMOUNT OF TIME WHEN IT IS SWITCHED ON.

Research is Required

The Japanese corporation, Matsushita (parent company of Panasonic), has years of data logging detailing how to apply UV to control various species.  But they too are keeping a tight grip on that data.  There are many combination of factors for a private researcher to consider: (Strength / distance of UV dose amount, time duration of UV dose, location of fixture and angles, continuous dose or intermittent dose, time in between doses, before or after germination, before or after fruiting, type of use such as disinfection, pretreatment, etc.)  And of course, safety mechanisms are a big part too.  Matsushita have developed a complete method based on their extensive research and applied it in real use with success.

However, once again, this is all Matsushita’s intellectual property.

What we do know about UV-C is that it controls smaller pests and pathogens very effectively when used correctly within the right parameters.  Furthermore we can see no reason why experienced growers who understand and appreciate how to use UV-C safely would not be able to determine their particular “sweet spot” for indoor garden pest and pathogen control and thus reduce their reliance on chemical insecticides.

We realize that using UV-C on plants is a highly controversial topic – so give us your opinion!  Do you think this is a step too far in the battle against pests?  Let us know: post a comment.

WORDS: Everest Fernandez