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

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

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

Why is RH so important?

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

What is Vapor Pressure Deficit (VPD)?

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

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

Managing Humidity

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

Humidification systems to increase RH.

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

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

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

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

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

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

Humidity’s Effect on Plants

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

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

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

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

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

Powdery Mildew from poor humidity control.

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

Quick reference chart:

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

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

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

Photos courtesy of AmHydro.

The 5 basics of recirculation and plant performance:

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

The Importance of Oxygen

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

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

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

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

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

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

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

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

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

Light

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

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

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

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

Temperature

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

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

Humidity

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

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

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

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

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

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

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

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

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

Air Circulation and CO2

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

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

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

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

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

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

The 5 basics of recirculation and plant performance:

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

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

Good luck and good growing.

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

The basics – What is NFT?

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

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

Why choose NFT?

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

NFT Gro-Tanks

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

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

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

Equipment

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

January 18th – Germination

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

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

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

January 31st – Propagation

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

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

February 4th – Growing on

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

February 5th – Setting up

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

February 14th – Vegetative Progress

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

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

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

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

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

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

February 25th – Flowers and Fruits

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

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

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

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

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

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

February 27th – Nutrient tweaking

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

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

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

February 29th – Roots going mad

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

March 3rd – Plant Training

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

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

March 11th – New plants!

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

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

March 14th – The Bumper Crop

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

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

March 26th – Growing on

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

Looking Ahead

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

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

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

What are Aphids?

Aphids (aka plant lice) are soft- bodied, pear-shaped insects that feast on your plants. Outdoors they are most prevalent during the spring and summer seasons. Aphids are common garden pests – the green variety is the most well-known, although they can also take pink, brown, yellow and black forms. In all, there are over 200 species of aphids. Some varieties are quite specific to certain plant groups, whereas most are not that fussy and will munch on a wide variety of different plants. Aphids are capable of asexual reproduction and can spawn throughout most of the year, sometimes producing nearly 100 young per aphid in the course of just one week! Indoor growers need to be especially wary of aphids. If you don’t spot them early, a relatively small intrusion will soon turn into a massive infestation unless you act quickly.

What’s the Damage?

Aphids injure your plants by puncturing plant stems and stalks with their skylets – powerful suction devices built into their mouths. Their goal is to find some plant sap which, once located, they suck mercilessly, gorging themselves at the plant’s expense. Prolonged aphid attacks will considerably weaken your plants. Common telltale signs of aphid damage include curled, discolored, and deformed leaves. Also, keep an eye out for “sooty mold” which is caused by mold colonies feeding off the sticky waste the aphids leave behind after their feeding frenzy. If all that isn’t enough, aphids can also spread incurable plant diseases. In short, aphids SUCK big time!

October 23

The wind began gusting with enough force to knock down my outdoor tomato plants. In order to save them, I had to continually move them in and out until the gusting ceased. It didn’t take long until the task of moving 40+ pots from the front yard into my two-bedroom apartment became onerous and inconvenient. Confronted with a living room and kitchen full of plants, I had no other place to put them than right in front of the door to my indoor garden. There (and everywhere in the house), my outdoor plants were spared from the 50-mile/ hour winds outside. I left them there for just over an hour. The strong winds passed so I proceeded to return all the plants outdoors. Little did I know that this would be the dumbest, most destructive thing I had ever perpetrated on my beloved tomato plants.

October 24

I woke up and began my regular morning watering of my outdoor plants. During this activity it’s not uncommon for me to spot the occasional caterpillar or earwig enjoying its breakfast, but today was different. Instead, I stumbled upon a family of aphids nesting on my tomato leaves. Temperatures had begun to hang in the 50s and 60s, and I was expecting the usual aphid wave that comes in the fall. So when I saw the little critters, I thought “well, the wave is here. I’ll start squishing aphids and wipe them out with some neem oil. No big deal.” And so I focused my attentions on pest control for my outdoor plants. And it worked! In less than two days’ time, my tomatoes appeared to be completely pest-free. Fortune, it seems, is not without a sense of irony.

October 28

Today was reservoir change day, always a logistically challenging endeavor considering how little room I have to move around in. First step is to empty my indoor garden of plants so that I stand a chance of reaching the ebb and flow table positioned against the far wall of my walk-in grow closet. As I moved and inspected the plants from the mid-section of the room I began to notice some light green bumps on the leaves of my sweet banana peppers. I got up close and saw these shiny, six-legged little critters standing on the leaves, their antennae bent towards their backs, gross-looking, and engaging in some serious sap-sucking. APHIDS! And if experience told me anything I knew that there were probably plenty more to be found. Sure enough, my heart sank when I discovered that all of the pepper plants on my ebb and flow table were populated with aphid “families.” Everything from my Dorset Nagas, my Ajíes Dulce and Caballeros, my Bhut Jolokias, and (oh, noooo!), some pimento plants that came from seeds saved by my late Grandmother – everything was covered in aphids! Panic eventually gave way to pragmatism. The remainder of the day was mostly taken up with bug-squishing and a frenzy of neem spraying. The reservoir change was postponed for another day or two. I had more pressing matters to attend to!

October 31

(photo courtesy of Flagstaffotos)

I woke up determined to get that reservoir change out of the way. I ventured into the bowels of my indoor garden and began to remove the plants from the tray as before. This revealed just how badly infested my plants were: colonies of aphids had pitched tents all over the plants’ leaves, stems and shoots. All of the lower leaves were suddenly looking really crappy: some had begun to show brown spots and the spotting looked like it was creeping upwards toward the plant canopy. Now I had a disease to identify on top of my aphid problem! It was not long before I identified the leaf spotting to be Anthracnose, a viral plant disease (for which there is no cure), which is often carried by aphids. That’s when the seriousness of the matter really struck home. My beautiful pepper plants were screwed. Even if I were to effectively eradicate what was now a full-blown plague of aphids, I’d still be left with sick plants! I’d screwed up royally by breaking that one important rule: Never bring outdoor plants into your indoor garden! If you absolutely have to, make sure they first undergo a lengthy quarantine period!

The plants had to be destroyed. Man, I was gutted. It didn’t matter so much that my Nagas were in the midst of setting fruit or that my pimentos had a special significance — all my infected plants had to be killed. So I took my camera and snapped a few shots of the unwanted guests and, without making too much of a stir, began to hack and bag branches until only the plants’ stems were left. All the containers were dumped – substrate n’ all – into a reinforced garbage bag. All infected plant matter was then doublebagged and immediately thrown in the dump outside. The reservoir was emptied and bleached thoroughly. The rest of the plants in my indoor garden were thoroughly inspected. Some contained one or two aphids, and were cleared of all visible pests and removed from the indoor garden. I sprayed a 10% bleach solution on the walls, floor and ceiling. All equipment inspected and sterilized. An hour of sparing an outdoor plant from wind damage had already compromised my whole indoor grow. This time I would leave nothing to chance.

After my indoor garden was cleaned, I re-checked all the plants and decided to just do away with any seedlings that showed signs of aphids or anthracnose. It would not be worth the time, effort and money to raise a plant that was doomed from the start. The rest of the plants were sprayed with neem oil in order to slow down the life cycle of any aphid youngling I could not catch. Inspections were performed daily until the problem was under control; I scheduled neem oil treatments every 3rd day, but this ended up being performed every other day due to the resurgence of young aphid colonies. Some leaves were beginning to appear rather leathery – probably because of the excess spraying of neem oil. At the end of that week I discovered some aphids nesting on the young shoots of my baobab tree. No other aphid affront had been this cheeky. I don’t mind admitting that the sight of more aphids at this point tipped me over the edge. It was time to call in the big guns.

November 2

I marched to my local hydro shop and made a beeline for the pest control aisle. There I picked up the largest can of pyrethrin-based spray. The store owner seemed surprised to see me buy a can of bug spray because I am a neem-type guy, so I let him in on the battle that was taking place in my indoor garden. He assured me that I had done all I could and that the bug spray would definitely take care of the problem. Once back home, I inspected all the plants and manually killed as many aphids as I could spot – only a handful at this point. This was good news as it indicated to me that the bulk of the infestation had been eradicated by disposing of the infected plants. Now my task was to prevent a re-infestation. In order to achieve this I had to do more than merely reduce their numbers: they needed to be obliterated!

The pyrethrin spray was applied after the lights went out, using short bursts and kept 1-2 ft away from the plants. This would ensure a more ample, gentler coverage while still delivering the pyrethrins to any potential pests. I sprayed my plants once again during mid-week and decided to wait a few more days and re-evaluate its effectiveness. My concerns about burning the plants dissipated throughout the upcoming week, as none of my plants showed signs of contact burn. Not only that, but I was seeing fewer & fewer aphids around the area, and my baobab tree exhibited none by the end of the week. Having seen good results from the pyrethrum spray, I decided to incorporate it into my pest control program. From then on, I would be lightly (but thoroughly) spraying my plants on a weekly basis.

Lessons Learned

There are lessons to be learned and relearned from our mistakes. My first mistake was the breaking of this most-important rule: Never bring outdoor plants into your indoor garden without first undergoing a quarantine period. You can also say that I screwed up by not destroying the pepper plants immediately after finding the first aphids indoors. But then again, no signs of Anthracnose were initially observed. I should have erred on the side of caution and assumed that where there are aphids, diseases follow. My third mistake was over-applying neem oil. Neem did not burn my plants, but it certainly turned my leaves hard and leathery (and I do not know if that is a good thing for their tiny, delicate stomata). However, all in all, I think I was lucky to have been able to control it by using pyrethrin; otherwise, all my plants would’ve been for the trash!

Moment of silence for Eliab’s loss. Now … got an aphid-assaulting tip or horror story you care to share? Post it below!

Source: Institute of Science in Society

“Major crops genetically modified for just two traits – herbicide tolerance and insect resistance – are ravaged by super weeds and secondary pests in the heartland of GMOs as farmers fight a losing battle with more of the same; a fundamental shift to organic farming practices may be the only salvation.”

- Dr. Mae-Wan Ho, Institute of Science in Society

Two traits account for practically all the genetically modified (GM) crops grown in the world today: herbicide-tolerance (HT) due to glyphosate-insensitive form of the gene coding for the enzyme targeted by the herbicide, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), derived from soil bacterium Agrobacterium tumefaciens, and insect-resistance due to one or more toxin genes derived from the soil bacterium Bt (Bacillus thuringiensis). Commercial planting began around 1997 in the United States, the heartland of GM crops, and increased rapidly over the years. By now, GM crops have taken over 85-91 percent of the area planted with the three major crops, soybean, corn and cotton in the US [1]] (see Table 1), which occupy nearly 171 million acres.

Table 1. GM crops grown in 2009 in the USA

The ecological time-bomb that came with the GM crops has been ticking away, and is about to explode.

HT crops encouraged the use of herbicides, resulting in herbicide-resistant weeds that demand yet more herbicides. But the increasing use of deadly herbicide and herbicide mixtures has failed to stall the advance of the palmer super weed in HT crops. At the same time, secondary pests such as the tarnished plant bug, against which Bt toxin is powerless, became the single most damaging insect for US cotton.

Monster plants that can’t be killed

It is the Day of the Triffids – not the genetically modified plants themselves as alluded to in John Wyndham’s novel – but “super weeds that can’t be killed” [2], created by the planting of genetically modified HT crops, as seen on ABC TV news.

The scene is set at harvest time in Arkansas October 2009. Grim-faced farmers and scientists speak from fields infested with giant pigweed plants that can withstand as much glyphosate herbicide as you can afford to douse on them. One farmer spent US$0.5 million in three months trying to clear the monster weeds in vain; they stop combine harvesters and break hand tools. Already, an estimated one million acres of soybean and cotton crops in Arkansas have become infested.

The palmer amaranth or palmer pigweed is the most dreaded weed. It can grow 7-8 feet tall, withstand withering heat and prolonged droughts, produce thousands of seeds and has a root system that drains nutrients away from crops. If left unchecked, it would take over a field in a year.

Meanwhile in North Carolina Perquimans County, farmer and extension worker Paul Smith has just found the offending weed in his field [3], and he too, will have to hire a migrant crew to remove the weed by hand.

The resistant weed is expected to move into neighbouring counties. It has already developed resistance to at least three other types of herbicides.

Herbicide-resistance in weeds is nothing new. Ten weed species in North Carolina and 189 weed species nationally have developed resistance to some herbicide.

A new herbicide is unlikely to come out, said Alan York, retired professor of agriculture from North Carolina State University and national weed expert.

Glyphosate-resistant weeds from widespread planting of HT crops

Glyphosate is the most widely used herbicide in the US and the world at large. It was patented and sold by Monsanto since the 1970s under the trade name and proprietary formulation, Roundup. Its popularity shot up with the introduction of HT crops. Data from the US Department of Agriculture indicate that the use of glyphosate on major crops went up by more than 15 fold between 1994 and 2005 [4]. The EPA estimated in 2000-2001 that 100 million pounds of glyphosate are used on lawns and farms every year [5], and over the last 13 years, it has been applied to more than a billion acres [6].

It did not take long for glyphosate-resistant weeds to appear, just as weeds resistant to every herbicide used in the past had appeared. The Weed Science Society of America reported nine weed species in the United States with confirmed resistance to glyphosate [6]; among them are strains of common ragweed (Ambrosia artemisiifolia), common waterhemp (Amaranthus rudis), giant ragweed (Ambrosia trifida), hairy fleabane (Conyza bonariensis), horseweed (Conyza canadensis), Italian ryegrass (Lolium multiflorum), johnsongrass (Sorghum halepense), rigid ryegrass (Lolium rigidum), and palmer pigweed (Amaranthus palmeri).

Glyphosate-resistant palmer super weed

Glyphosate-resistant palmer pigweed first turned up in late 2004 in Macon County, Georgia, and has since spread to other parts of Georgia as well as to South Carolina, North Carolina, Arkansas, Tennessee, Kentucky and Missouri [7]. An estimated 100 000 acres in Georgia are severely infested with pigweed and 29 counties have now confirmed pigweed resistance to glyhosate, according to weed specialist Stanley Culpepper at the University of Georgia. In 2007, 10 000 acres of glyphosate-resistant pigweed infested land were abandoned in Macon County.

Monsanto’s technical development manager Rick Cole was reported saying that the problems were “manageable”. He advised farmers to alternate crops and use different makes of herbicides. Monsanto sales representatives are encouraging farmers to mix glyphosate and older herbicides such as 2,4-D, banned in Sweden, Denmark and Norway on account of links to cancer and reproductive and neurological damages. It is a component of Agent Orange used in Vietnam in the 1960s.

Farmers in Georgia are reported to be going back to conventional non-GM crops.

Weed scientists at the University of Georgia estimate that an average of just two palmer amaranth plants in every 6 m length of cotton row can reduce yield by at least 23 percent [8]. A single weed plant can produce 450 000 seeds. Many fields in Arkansas, Tennessee, New Mexico, Mississippi and most recently, Alabama are also infested.

Paraquat is recommended for use in conservation tillage programmes, mixed with up to three other herbicides, each with a different mode of action. Scientists at the University of Tennessee have seen palmer weeds resistant not only to glyphosate but also to the sulfonylurea herbicide trifloxysulfuron-sodium.

Glyphosate resistance with the greatest of ease

Critics have been predicting glyphosate-resistant weeds before HT crops were introduced, simply through cross-pollination between HT crops and wild weedy relatives. But they had neglected the ‘fluid genome’ mechanisms that can alter genomes and genes in response to environmental stimuli, enabling most weed plants to become herbicide resistant independently of cross-pollination. I drew attention to these mechanisms in my book Genetic Engineering Dream or Nightmare, the Brave New World of Bad Science and Big Business [9] first published in 1997/1998.

Researchers led by Todd Gaines at Colorado State University, Fort Collins in the United States investigated glyphosate-resistant palmer pigweed populations from Georgia. They found that the gene coding for the enzyme EPSPS responsible for metabolising glyphosate herbicide was amplified (multiplied) 5 to 160-fold in glyphosate-resistant plants compared with glyphosate-susceptible plants [10]. The level of gene expression was positively correlated with gene copy number. Fluorescent staining for the gene showed that the amplified gene copies were present on every chromosome.

Gene amplification is one of the most common physiological responses of cells and organisms to ‘selective’ agents in their environment, known at least since 1980s [9].

Glyphosate resistance has been confirmed in 16 weed species as of 2009 [10]. The mechanisms identified so far include reduced glyphosate uptake, and/or mutations in the EPSPS gene that make it less susceptible to inhibition by the herbicide. Glyphosate-resistant palmer pigweed is the first case of resistance based on gene amplification. It confirms the ease with which resistance to obnoxious agents can evolve [9], and the futility of this ‘chemical warfare’ against nature.

Tarnished plant bug the single most damaging pest for cotton

The tarnished plant bug infested 4.8 million acres of US cotton in 2008 [11] making it the single most damaging pest for cotton. Another insect, the fleahopper ranked 5th, and infested 2.3 million acres.

The Cotton Belt of the United States, extending from the San Joaquin Valley of California to Southeastern Virginia, has largely seen off the boll weevil and tobacco budworm since the introduction of Bt cotton, which now accounts for 65 percent of the area planted with cotton (Table 1 [1]). But, as in India and elsewhere [12, 13] (Farmer Suicides and Bt Cotton Nightmare Unfolding in India, Mealy Bug Plagues Bt Cotton in India and Pakistan, SiS 45), secondary pests are posing serious problems, especially the tarnished plant bug.

The tarnished plant bug (TPB), Lygus lineolaris, has been a cotton pest for as long as records were kept. Before 1995, it was controlled with insecticides targeting other insect pests such as tobacco budworm and boll weevil. According to researchers at the Mississippi State University Delta Research and Extension Center [14], since the widespread adoption of Bt-cotton and eradication of the boll weevil, less insecticide have been used; and as a result, the tarnished plant bug has become the primary insect pest of cotton.

Additional insect control costs are coming from increasing foliar sprays, higher technology fees and pest resistance, said Jeff Gore, research entomologist at the Delta Research and Extension Center, speaking at the 2010 Beltwide Cotton Conferences in New Orleans [15]

In 1995 planting an acre of cotton cost $12.75 to $24; in 2005, planting Bollgard, Roundup Ready cotton with a ‘Cadillac’ seed treatment would have cost about $52 an acre. Now in 2010, with Bollgard II and Roundup Ready Flex, farmers will be spending $85 or more an acre.

“In Mississippi, we have growers who are spending well over $100 for foliar insect control. You add that onto technology fees and seed treatments, you understand why our cotton acreage is decreasing.” Gore said.

To compound the problem, TPB has become resistant to several classes of insecticides, particularly in the Delta regions of the Mid-South states [14].

While TPB is a pest of cotton throughout the growing season, it is particularly damaging during the flowering period, when the pest reproduces copiously, so both adult and immature stages of TPB feed on cotton during the flowering period. Most feeding occurs on reproductive structures. The pests insert their mouthparts into squares and small bolls. It is not uncommon for TPB to cause near-total crop loss in the absence of effective control in some areas of the Delta.

Mid-South growers consulted Gore about planting a non-Bt variety, especially with the higher costs of Bt technology [15]. “We have a few growers planting small acreages of non-Bt cotton, and they’re probably going to see benefits from that.

“But if we start shifting back to non-Bt cotton, I promise you, the tobacco budworm will come back, and we don’t want to be making foliar applications for resistant tobacco budworms, in addition to treating tarnished plant bugs. The amount of money we would have to spend in that situation would be astronomical.”

TPB has been the No. 1 pest in the Mid-South for the past four to five years, and is driving a lot of cotton growers out of the Mississippi Delta, no longer able to afford the cost of sprays.

Gore revealed that spider mites are also gaining a reputation as ‘budget busters’ in the South, along with aphids and stink bugs.

Like TPB, spider mites are becoming resistant to the insecticides used to control them. “Over the past 15 years, we’ve essentially doubled our application rates with Bidrin and tripled our application rates with acephate. So we’re not only spraying more often, we’re applying higher rates that cost more.” Gore said.

He pointed out that a side-effect of relying on neoniccotinoids for plant bug control is some resistance has developed in cotton aphids. “We’re starting to hear lots of complaints from consultants across the Mid-South.”

More of the same is futile

It is disappointing though predictable that the only official academic advice given to farmers is more of the same conventional practices that created the problems in the first place, spraying more and spraying mixtures of different kinds of pesticides, including those banned for being too toxic. Industry, meanwhile, is ready to sell varieties with more stacked GM traits; up to eight at double the seed price [16].

Disappointing too is the persistent effort by some governments and government scientists to promote the failed GM technology, which as I made clear, was already obsolete since the early 1980s [9]. A Sciencexpress paper (indicating quick publication, probably without peer review) entitled “Food security: the challenge of feeding 9 billion people” [17] co-authored by UK chief scientist Prof. John Beddington among others, while somewhat dismissive of current GM crops, nevertheless holds out promises we’ve heard for more than 30 years. “The next decade will see the development of combinations of desirable traits and the introduction of new traits such as drought tolerance. By mid-century much more radical options involving highly polygenic traits may be feasible.” It went on to promise “cloned animals with engineered innate immunity to diseases” and more.

Glyphosate and Roundup, still advertised as ‘less toxic to us than table salt’ in a pamphlet from the Biotechnology Institute promoting HT crops as ‘Weed Warrior’ [18], is in fact highly toxic as new findings indicate [19, 20] (Death By Multiple Poisoning, Glyphosate and Roundup, SiS 42; Ban Glyphosate Herbicides Now, SiS 43). Thirteen years of GM crops in the USA has increased overall pesticide use by 318 million pounds [21] (GM Crops Increase Herbicide Use in the United States, SiS 45). The extra disease burden on the nation from that alone is considerable.

India has learned bitter Lessons from Bt Cotton [22] in a saga of worsening farm suicides and, in common with the USA, an ecological disaster in secondary and new cotton pests, resistant pests, new diseases, and above all, soils so depleted in nutrients and beneficial microorganisms that they would cease to support the growth of any crop in a decade. Their only salvation is a return to organic agriculture, which has already proven far more sustainable and profitable than Bt cotton [12]. This may apply also to the USA.

A fundamental shift in farming practices needed now

The organic market has been booming in the United States despite the economic downturn. According to a new report from the US Department of Agriculture, retail sales of organic food went up to $21.1 billion in 2008 from $3.6 billion in 1997 [23] (see Fig. 1). The market is so active that organic farms have struggled at times to produce sufficient supply to keep up with the rapid growth in consumer demand, leading to periodic shortages of organic products.

Figure 1 Growth in US organic market 1997 to 2008

Certified organic acres more than doubled from 1.3 million acres in 1997 to a little over 4 million acres in 2005 (0.5 percent of all agricultural land in the US). In the same period, the number of organic farms increased from 5 021 to 8 493, and the average size of certified organic farms went from 268 acres to 477 acres.

So why are US farmers failing to taking advantage of the rapidly expanding market? It is thought [23] that potential organic farmers may opt to continue with conventional production methods because of “social pressures from other farmers nearby who have negative views of organic farming”, or because of an inability to weather the effects of reduced yields and profits during the transition period. This is not surprising on account of the persistent negative propaganda carried out by GM proponents, including government regulatory agencies, against organic agriculture. (See for example the recent attempt by UK Food Standards Agency to prove organic food is no more nutritious than conventional food, which backfired [24] (UK Food Standards Agency Study Proves Organic Food Is Better, SiS 44). The usual claims are that organic agriculture yields less and require more energy than conventional agriculture, and organic produce no more nutritious or healthy, but less hygienic than conventional produce. These false claims are all thoroughly refuted in ISIS report Food Futures Now: *Organic *Sustainable *Fossil Fuel Free [25], with evidence from the published scientific literature, as well as other studies.

Most relevant for US farmers is a study by Kathleen Delate of Iowa State University and Cynthia A. Cambardella of the US Department of Agriculture assessing the performance of farms during the three-year transition it takes to switch from conventional to certified organic production [26]. The experiment lasting four years (three years transition and first year organic) showed that although yields dropped initially, they equalized in the third year, and by the fourth year, the organic yields were ahead of the conventional for both soybean and corn.

Our report [25] also documents the enormous potential for reducing greenhouse emissions – even to the extent of freeing us entirely from fossil fuels – through organic agriculture and localised food (and renewable energy) systems. It is a unique combination of the latest scientific analyses, case studies of farmer-led research, and especially farmers’ own experiences and innovations that often confound academic scientists wedded to outmoded and obsolete theories, of which GM technology is one glaring example.

At about the same time our report was released, the International Assessment of Agricultural Knowledge, Science and Technology for Development (IAASTD) was also published. IAASTD was the result of three-year deliberation by 400 participating scientists and non-government representatives from 110 countries around the world [27]. It came to the conclusion that small scale organic agriculture is the way ahead for coping with hunger, social inequities and environmental disasters [28] (“GM-Free Organic Agriculture to Feed the World”, SiS 38).

A fundamental shift in farming practice is needed right now, before the agricultural meltdown is complete.

References

1. Adoption of genetically engineered crops in the U.S.: Extent of adoption. USDA Economic Research Service, 1 July 2009, http://www.ers.usda.gov/Data/biotechcrops/adoption.htm
2. Super weed can’t be killed, abc news, 6 October 2009, http://abcnews.go.com/Video/playerIndex?id=8767877
3. “N.C. farmers battle herbicide-resistant weeds”. Jeff Hampton, The Virginian-Pilot. 19 July 2009, http://hamptonroads.com/2009/07/nc-farmers-battle-herbicideresistant-weeds
4. Who benefits from gm crops? The rise in pesticide use, executive summary, Friends of the Earth International, Amsterdam, January 2008.
5. 2000-2001 pesticide market estimates: usage, U.S. Environmental Protection Agency, http://www.epa.gov/oppbead1/pestsales/01pestsales/usage2001_3.htm
6. Glyphosate-resistant weeds: can we close the barn door? Weed Science Society of America, 18 November 2009, http://www.wssa.net/WSSA/PressRoom/WSSA_GlyphosateResistance.pdf
7. “’Superweed’ explosion threatns Monsanto heartlands”, Clea Caulcutt, 19 April 2009, http://www.france24.com/en/20090418-superweed-explosion-threatens-monsanto-heartlands-genetically-modified-US-crops
8. “Paraquat fights glypohsate resistant palmer amaranth”, 30 September 2009,

http://paraquat.com/english/news-and-features/archives/paraquat-fights-glyphosate-resistant-palmer-amaranth
9. Ho MW. Genetic Engineering Dream of Nightmare? The Brave New World of Bad Science and Big Business, Third World Network, Gateway Books, MacMillan, Continuum, Penang, Malaysia, Bath, UK, Dublin, Ireland, New York, USA, 1998, 1999, 2007 (reprint with extended Introduction). http://www.i-sis.org.uk/genet.php
10. Gaines TA, Zhang W, Wan D et al. Gene amplification confers glyphosate resistance in Amaranthus palmeri. PNAS Early Edition 2009, www.pnas.org/cgi/doi/10.1073/pnas.0906649107
11. ARS survey helps growers track two key cotton pests. PHYSORG.com, 1 December 2009, http://www.physorg.com/news178912351.html
12. Ho MW. Farmer suicides and Bt cotton nightmare unfolding in India. Science in Society 45 (in press)
13. Ho MW. Mealy bug plagues Bt cotton in India and Pakistan. Science in Society 45 (in press)
14. Catchot A, Musser F, Gore J, Cook D, Daves D, Lorenz G, Akin S, Studebaker G, Tindall K, Stewart S, Bagwell R, Leonard BR and Jackson R. Midsouth Multtistate Evaluation of Treatment Thresholds for Tarnished Plant Bug. 2009, Mississippi State University Extension Service, http://msucares.com/pubs/publications/images/p2561_pics/bug_1.jpg
15. “Insect control pushes cotton costs higher”, Elton Robinson, Farm Press, 15 January 2010, http://deltafarmpress.com/cotton/cotton-insect-control-0115/
16. Benbrook C. Critical issue report: the seed price premium. The Organic Center. 2009 December. http://www.organic-center.org/reportfiles/Seeds_Final_11-30-09.pdf
17. Godfray HCJ, Beddington JR, Crute IR, Haddad L, Lawrence D, Muir JF, Pretty J, Robinson S, Thomas SM and Toulmin C. Food security: the challenge of feeding 9 billion people. Sciencexpress, 28 January 2010/10.1126/science.1185383
18. Weed Warrior Hebicide-Tolerant Crops, accessed 29 January 2010, http://www.biotechinstitute.org/resources/YWarticles/10.1/10.1.3.pdf
19. Ho MW and Cherry B. Death by multiple poisoning, glyphosate and Roundup. Science in Society 42 , 14, 2009
20. Ho MW. Ban glyphosate herbicides now. Science in Society 43, 34, 2009
21. Cherry B. GM crops increase herbicide use in the United States. Science in Society 45 (in press)
22. Ho MW. Lessons from Bt cotton. ISIS letter to Hilary Benn, UK Secretary of State for the Environment, 4 January 2010, http://www.i-sis.org.uk/lessonsFromBtCotton.php
23. Marketing U.S. organic foods: recent trends from farms to consumers. Carolyn Dimitri and Lydia Oberholtzer, USDA Economic Research Service, September 2009, http://www.ers.usda.gov/Publications/EIB58/
24. Ho MW.UK Food Standards Agency study proves organic food is better. Science in Society 44, 32-33, 2009.
25. Ho MW, Burcher S, Lim LC, et al. Food Futures Now, Organic, Sustainable, Fossil Fuel Free, ISIS and TWN, London, 2008. http://www.i-sis.org.uk/foodFutures.php
26. Delate K and Cambardella CA. Organic production: Agroecosystem performance during transition to certified organic grain production. Agronomy Journal 2004, 96, 1288-98.
27. International Assessment of Agricultural Knowledge, Science and Technology for Development, IAASTD, 2008, http://www.agassessment.org/index.cfm?Page=Press_Materials&ItemID=11
28. Ho MW. “GM-free organic agriculture to feed the world”. Science in Society 38, 14-15, 2008.

Both are beneficial fungi found naturally in soil. Trichoderma are more for cycling nutrients in the soil and providing protection against soil pests (but you will seldom find it labeled as a pest control) while mycorrhizal fungi help more with nutrient and water uptake and increased root growth. Both combined will promote a very healthy root system overall.The two work together well. Trichoderma help make nutrients soluble. Mycorrhizal fungi can actually take the nutrients up and translocate them into the plant.

Q. How do I successfully introduce and propagate mycorrhizal fungi in my hydroponic garden?

Mycorrhizal fungi can be mixed directly with soil-less media or added to the nutrient solution directly just like any regular powder supplement. There is a myth that you cannot use mycorrhizal fungi with synthetic / mineral-based nutrients, but this is not true. Mycorrhizal fungi can be used with soil, hydroponics and cuttings. The key benefits in hydroponics are extended root systems (which naturally lead to an increase in yield), not to mention protection against root zone pests and diseases. Imagine miles of mycorrhizae hyphae exploring the nutrient resources. Mycorrhizal fungi cause roots to branch and form more fine feeder roots that can go after nutrients and minerals.

Q. Should I feed mycorrhizae carbs? (e.g. molasses?)

Molasses and other carbs are good for feeding bacteria and other types of fungi. But you don’t need to feed the mycorrhizae. That’s missing the point. The plant feeds them! It’s the exudates from the plant roots that cause the mycorrhizal propagules to germinate. (There are synthetic compounds that cause the mycorrhizae to germinate but they are unnatural, expensive and not commonly available.) You are better off adding products which contain humic acids (organic growers can use high quality organic inputs such as North Atlantic sea kelp) to promote more root exudates (food for the mycorrhizae).

Q. What hydroponic growth media do mycorrhizae prefer?

Mycorrhizal fungi can create mycelial networks in soil, coco coir, rockwool and many other inert growth media. They can even survive in a totally aqueous environment, as long as it is properly aerated, but they will not replicate. Mycorrhizae will grow and increase in biomass only once they are attached to a plant root.

Q. What about mycorrhizal fungi and high phosphorous levels?

Mycorrhizae fungi spores ‘sleep’ while levels of phosphorus are high (above 70ppm). They only awaken when levels drop lower than this. This is another reason to establish your mycorrhizae as early on in the plant’s development cycle as possible.

Q. What conditions do mycorrhizal fungi prefer?

Temperature: around 68-73°F is ideal but mycorrhizae can also help your plants tolerate occasional temp extremes.

Moisture: mycorrhizal fungi like to have a good air/water mix to thrive. Too moist or too dry is not ideal. Once again, they will help the plant tolerate any extremes that occur.

pH: it depends on the mycorrhizae species but generally they thrive in 5.5-7.5. Some can tolerate acidic conditions better than others while some like alkaline better than others. Look for products that are made from a blend of different species in order to create a healthy mycorrhizae population that will thrive in varying pH conditions.

Q. What conditions should be avoided?

Very high temperatures. (135- 140°F will definitely start killing them off but then, at those temperatures, the happiness of your fungi is the least of your problems!) The less chlorine your water contains, the better for both fungi and plants too. However, typical levels of chlorine from municipal supplies should not cause a problem.

Q. When should I start using mycorrhizal fungi?

As soon as possible! It takes less mycorrhizae to colonize a juvenile plant than a larger one. Commercial growers have negated the cost of mycorrhizal fungi with their increased seed germination rates. It takes a couple of weeks to form on the roots after the first inoculation so get the process started right at the seedling / cutting stage. The trick is to introduce the mycorrhizal fungi spores as early as possible to give them time to establish themselves. This is particularly important if you are growing short-cycle plants.

Q. Do mycorrhizal fungi need to be reintroduced on a regular basis? Do I need to add it more frequently than once with every nutrient change?

Best performance is achieved with numerous applications throughout the growth cycle. You can’t really overdo mycorrhizae. If there are more roots producing more exudates it will probably help to add more mycorrhizae. But don’t bother any later than 2-3 weeks before harvest. It’s a waste of time. Your mycelial network should already be established. It won’t do any harm to keep using it (and often the instructions on the mycorrhizae product will encourage you to!), but you’re just wasting your money! Adding it with every nutrient change won’t do any harm either. It’s just a question of minimizing waste. A good tip is to mix the fungi in a one gallon jug to get it nicely diluted, then pour it into your nutrient solution. Otherwise the powder can sit at the bottom of the res. The white powder you sometimes see at the bottom of your res is just the carrying agent of the spores, not the spores themselves.

Q. What mycorrhizae products can I find in my local grow store?

You’d best ask down at your store! You’ll most likely find a few different brands. The products usually come as a jar of white powder – this is a ‘carrying agent’ for the spores. If you want to compare products, look for the number of mycorrhizal species per pound and the diversity of species. Oh, and the price!

Q. Ok, but how do I actually use mycorrhizal fungi to benefit my plants?

Mycorrhizal application is easy and requires no special equipment. The goal is to create physical contact between the mycorrhizal inoculant and the plant root. Mycorrhizal inoculant can be sprinkled onto roots during transplanting, worked into seed beds, blended into loose growth media, “watered in” via existing irrigation systems, added directly to the nutrient solution, applied as a root dip gel or even probed into the root zone of existing plants. Most hydroponic growers simply add the fungi by diluting the powder holding the spores into some water and adding this to their nutrient solution. It’s very easy.

Q. Do mycorrhizal fungi actually guard the roots against other nasties? If so, which nasties exactly?

Yes. Nasties include: rhizoctonia, fusarium, pythium and phytophthora. They can also mitigate the detrimental effects of high salt conditions.

Q. How exactly do mycorrhizal fungi guard the roots? Do they simply ìcrowd outî the root zone or is it more complex?

Endo mycorrhizal fungi thicken the cell walls around the root cortex making it harder for pathogens to penetrate. They also compete with pathogens for some of the same food sources. Mycorrhizal fungi help with antibiotic production, armoring of roots with chitin, and control of excess nutrients.

Q. What’s the difference between “endo” and “ecto” mycorrhizal fungi?

Endo = has an exchange mechanism inside the root (and hyphae extends outside of the root). Ecto= lives only outside the root. The endo mycorrhizae form with mostly green, leafy plants and most commercially produced plants. Ecto mycorrhizae form with mainly conifers and oaks: more woody plants. Endos are for everything else. In hydroponics, ectos don’t even matter. Fruits, veg, flowers … stuff we love to grow … they love endo.

Q. Are there any differences in how the hydroponic grower should use mycorrhizal fungi compared with the organic grower?

Both types of grower need to get the inoculum near roots. Same product, same application rates. Same number of spores per square foot. Both types of growers can reduce their nitrogen and phosphorus inputs.

Q. Do mycorrhizal fungi help with nutrient extraction in a hydroponic environment or are they more relevant in soil / organics where nutrients need to be broken down first in order to become available?

Mycorrhizal fungi are just as effective in hydroponic applications as they are in organics / soil. A main function of mycorrhizal fungi is phosphorus uptake. It’s important to have a good colonization and a good mycorrhizal fungi “web” already established before you go into flowering.

Fascinated? We are! Be sure to check out “Superfeeding” by Mike Amaranthus and John Eagen for more information on using mycorrhizea to benefit your indoor garden!

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.

Supercharged plants.  Sounds rather pleasant doesn’t it?  But what exactly are we talking about? A supercharged growing environment is one where no single thing your plants need is in short supply.  Think of it like a series of links in a chain.  The rate of your plants’ development is only ever going to be as fast as the weakest link allows.

So what are these links?  Well, the obvious examples include: plant genetics, light levels, temperature, CO2, and relative humidity.  The not so obvious example is oxygen.  This odorless, colorless gas plays a critical role in plant growth and bloom.  In fact, despite being all around us, it could be the crucial component that is holding your plants back…

WORDS: Jim Lepard

The Key Benefits of Oxygen for Plants

Oxygen usually makes up 45% of the dry tissue weight of a plant.  It is a macro-element, along with nitrogen, phosphorus, hydrogen, carbon, potassium, calcium, sulfur and magnesium.

Oxygen provides essential energy for plants to turn their sugars into cell structure.  In other words, plants need oxygen to grow!  Oxygen is also used by plants to control their stomata – tiny but crucial “breathing apparatus” in their leaves.

We tend to think of plants creating oxygen as the end product of photosynthesis but, as with many natural processes, the complete picture is more cyclical.  Plants also use oxygen in two major ways.  They uptake it through their roots and they absorb it via their leaves.

At night most plants reverse the process of photosynthesis and switch to burning carbohydrates and oxygen while producing carbon dioxide and water. So it’s important to make sure that oxygen levels are maintained in the indoor garden, especially at night when plants aren’t producing it via photosynthesis.  Most growers achieve adequate levels of oxygen at night by using extraction fans to bring in a steady supply of fresh air.

Oxygen and Stomata

Stomata consist of pores called stoma, which are bordered by two specialty guard cells. The guard cells regulate the size of the opening of the stoma (pore).  Because the stoma is responsible for the exchange of gases (i.e. oxygen and CO2) plus water vapor, it is critical that stomata are healthy and working properly.  If the stomata are oxygen deprived from the root zone, they begin to shut down and the size of the stoma opening becomes smaller due to the loss of turgor pressure in the stomata guard cells, restricting the exchange of gases and water vapors.  If the flow of water slows in the plant, the plant cannot cool itself and begins to suffer from overheating – visually apparent from wilting.  The uptake of nutrients in the water is also affected, along with the flow of oxygen.  This further compounds the problem, resulting in necrosis of the plant’s leaves. Photosynthesis is slowed as well, leaving the plant sick and weak, unable to fight off insects and disease, resulting in lower yields and eventual death of the plant.

Dissolved Oxygen

Many growers overlook the importance of dissolved oxygen levels in their nutrient solution.  When oxygen levels in a nutrient solution are raised, you essentially give your plants the ability to process more gases and water vapors, resulting in a cooler, faster growing and higher yielding plant. Root systems work more efficiently when highly oxygenated.  This is because oxygen affects the electrical charge of water and nutrients allowing the roots to uptake using less energy.

Increased oxygen levels also help to reduce water borne pathogens and fungi, such as the dreaded pythium and saprophytic fungi.  By elevating oxygen levels, the grower instantly creates a more suitable environment for aerobic bacteria (our friends). The more friendly bacteria we have, the greater their effectiveness in combating any anaerobic bacteria (our enemy).

Cooler water is capable of holding on to more oxygen than warmer water.  So when a nutrient solution starts to warm up, its ‘hold’ on dissolved oxygen decreases. For example, the oxygen content of a fully aerated solution 68°F (20°C) is around 9ppm, whereas at 86°F (30°C), it drops by over 16% to 7.5ppm.

Popular Methods of Increasing Oxygen Levels
Growers who appreciate the importance of dissolved oxygen have historically tried a variety of methods to increase levels in their nutrient solution.  It’s fairly straightforward to improve levels, but far harder to achieve ‘supercharged’ levels.

1. Surface to Air Contact
A submersible pump is placed into the nutrient reservoir.  When switched on it creates turbulence in the nutrient solution which increases its contact with air. The barrier between the water and air is broken (like a waterfall hitting a pool) allowing oxygen to be absorbed into the water.  The more turbulence at the surface, the greater the oxygen absorption.

2. Forced Aeration and Air Stones
This is one of the most popular methods used by growers today. Air pumps or compressors are used together with air stones or perforated pipe placed in the bottom of the nutrient tank. An air stone is traditionally a piece of limewood or porous stone but can also be made from fiberglass.  When air is pumped into the stone it creates very fine bubbles.  As these fine bubbles rise in the nutrient tank, some of the oxygen is absorbed by the nutrient solution.

There is currently some controversy surrounding the efficacy of air stones.  One theory suggests that larger bubbles rising in the nutrient solution absorb smaller suspended bubbles on their way up and air dissipates out of the solution.  In one test the oxygen levels in a nutrient solution actually dropped after running the air stone for 50 minutes!  Other growers (and aquarium owners) swear by them!

3. H2O2  (Hydrogen Peroxide)
Hydrogen Peroxide is known for increasing oxygen levels and its high oxidizing properties.  When H2O2 is first introduced to the nutrient solution there is a spike in oxygen levels and the plants receive a boost of oxygen.  However, the oxygen levels quickly drop off, especially with an air pump and aeration or agitation of the water via a water pump circulating through the system.  Along with the higher amount of oxygen, comes the high level of oxidization.  This is fine if the plants are suffering from any fungi or pathogens that may be in the system.  However the indiscriminating oxidizing effect of H2O2 can also attack a healthy root system.

Double air diffuser

4. Air Diffusers
The large scale solution.  Air diffusers force concentrated atmospheric oxygen into the nutrient solution. These systems achieve very high oxygen levels but they have to be regulated carefully and tend to be used by large commercial greenhouses that can afford the room and cost of such equipment.

5. Electrolysis
Oxygen is produced through electrolysis when a DC current is passed through an anode and cathode in an acid or salt solution.  As the solution passes by the anode and cathode the current separates the oxygen atom from the hydrogen atoms at a molecular level, leaving the oxygen suspended in the water. The plant absorbs some of the beneficial hydrogen but because hydrogen is 16 times lighter than oxygen, most of it is disbursed through the surface of the water.  The benefit of this method of raising oxygen levels in a nutrient solution is that oxygen is not being forced into the water.  The oxygen is actually being generated from the water, within the water.

Still not convinced about the importance of oxygen?  Then check out this basil crop, brought back from the brink of death after a spell of freakishly hot weather!  How? Oxygen levels were raised in the nutrient solution using electrolysis. The basil was infested with pythium (root rot) but started to recover almost immediately!

Healthy white roots appearing days after the nutrient solution was regularly treated with oxygen electrolysis.

Basil roots 10 days after the beginning of electrolysis treatment.

Incredible! After being all but overcome by pythium, the roots of this basil plant have been restored to health after 21 days of electrolysis treatment.

If your plants are not fighting root rot and disease, there’s no doubt that you will harvest bigger, heavier crops – without the need for chemical pesticides or supplements.

Now take a deep breath. Feels good, doesn’t it?

Warning – Incorrect Use of Some Restricted Pesticides Can Create “Superbugs”

In today’s marketplace where governments are banning hundreds of insecticides, fungicides and biocides, the consumer is now only being offered a few products that will control plant-eating insects albeit some are a lot more effective than others.  Commercial growers are offered some restricted products that are not available to regular hobby growers. These restricted products are part of an IPM (Integrated Pest Management Program) and are only to be used by licensed professionals that have the appropriate application equipment and health preventative measures in place to assure them of not being poisoned in addition to the application knowledge on how to use these products properly.

Some hobby growers are managing to obtain restricted pesticides and using them in their indoor garden.  The consequences are more far reaching than you might first think.  It’s not just the health risk to the hobbyist grower and food consumer.  Due to the grower’s lack of knowledge on how to correctly apply these licensed products according to the label’s instructions (and as part of a Total Environmental Integrated Pest Management Program), they are inadvertently creating “superbugs” – pests with increased resistance to insecticide.  A few of these products are AVID ™, MONITOR™ (STINK), FLORAMITE™ and VENTEX™.

Unless you really know what you are doing with these licensed insecticides you could merely be eliminating the weakest pests and leaving, say, the strongest 0.1% to breed with each other.  The result is a hardcore “superbug” that, through an accelerated process of natural selection, has an inbuilt resistance to the original pesticide product.

The worst superbug of them all?  You guessed it –the spider mite.  These are the insect pests that invariably create the most damage in indoor gardens.  Currently in California there is much talk among indoor gardeners about the infamous “Mendo Mite” – a super breed of spider mite that is believed to have originated in Mendocino County which has vastly increased resistance to pesticides.

In Canada there are no registered bio-pesticides to kill spider mites – as these are new products that do not have enough trial studies undertaken to complete an application proving efficacy, toxicity and several other criteria that are demanded by Health Canada.

Safer Alternatives

Neem oil is a good deterrent but will not kill spider mites. Neem oil works primarily as a systemic. A systemic pesticide is watered into the root base or applied through a foliar spray. Once the physical properties of the neem oil have been absorbed into the vascular structure of the plant (10-14 days after application) the taste of the foliage is not attractive to the spider mites so they will go elsewhere for their food. The other benefit of neem oil is it will make a lot of leaf-eating insect’s molt.  Molting in layman terms is a vasectomy. The adult insects that ingest foliage treated with neem oil will be incapable of laying eggs thus eventually reducing the population of the spider mites.

The immediate drawback to using neem oil is the time delay before it becomes effective.  If you discover an infestation today it will not help you through this crucial elimination period.  In addition it can impart flavors to your crops. Foliar applications of neem oil also clog stomata (the “breathing part of a plant’s leaves) which slows photosynthesis resulting in late harvests. Overall neem oil is a good addition to most gardens but you may consider discontinuing its use at the early stages of the flowering cycle.

Insecticidal soaps are simply soaps that, if used on a strict daily basis, may give you some results. However, these new superbugs are pretty tough and may show a lot of resilience to insecticidal soap application. The other drawback of insecticidal soaps is that they cause phyto-toxicity (damage to plant tissue) and that they do not kill insects on contact. A thorough application is always required in order to be effective – so much that it is running off the plant – then it drowns the insect but secondly causes clogged stomata in a similar manner to neem oil, thus delaying the harvest.

Pyrethrums are a botanical extract and the most effective measure to eliminate spider mites quickly. Pyrethrum is available in a couple formats – as a dust or an aerosol spray – cans or plastic pump spray bottles.  Due to pyrethrums decomposing rapidly in humid, high temperatures and windy areas the powder is the least effective as it is a contact application only and dusting a plant on all sides is not that easy as you are working against gravity from the onset!  And experienced growers all know that most spider mites (super or otherwise!) will be found on the underside of foliage – the powder simply will not reach or stick.

Most indoor gardeners agree that pyrethrum aerosol sprays are the most effective. Using pyrethrum gives you immediate results – instantly killing every insect that it contacts. The drawback is that, as an evolutionary defense, when spider mites smell pyrethrum they lay eggs as they know they are going to die.

Pyrethrum used once every three to four days for four consecutive applications will result in eliminating the lifecycles of the spider mites and will eradicate them completely from your garden.

Have you been hit by the “Mendo Mite” or with any other “superbug” that appears to have increased resistance to pesticides?  Tell us about it below!

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