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.

Is your back aching from lugging endless sacks of soil, coco or other growth media in and out of your indoor garden? Then check out our latest blueprint, aptly named “The Water Room.” The idea is to grow monster tomato plants directly in a nutrient solution using a cutting-edge, modular Deep Water Culture (DWC) system called The Under Current™. But the liquid theme doesn’t end there. Water is also used to cool the garden using an ingenious chiller-based system created by Hydro Innovations.

Everest catches up with Dan and Stephen, the co-designers of this blueprint, to find out what logic exists beyond all this liquid!

GROWING IN WATER

Everest: Hi Dan. Let’s start by looking at the systems themselves. Am I right in thinking each 16 pot system requires both an air pump and a water pump?

Dan: That’s right, Everest. The inline water pump powers the negative solution displacement, which drives the Sub Current Culture (SCC) method. The linear, high efficiency air pumps provide the active aeration which supercharges the nutrient uptake.

Everest: So it runs 24/7 – even during the night cycle?

Dan: In properly aerated and balanced nutrient solution, plant roots can stay submerged 24/7, even through the dark cycle. Plants continue to metabolize nutrients and exchange gases in the dark, so keeping the solution moving aids in these processes. And remember, no timers for pumps means no worries!

Everest: How much solution is in each module?

Dan: We recommend an operating volume of approximately six gallons per module. That makes 100 gallons +/- in a 16XL (6 x 17 modules). A very small volume of solution is held in each joint (conduit) between the modules as well.

Everest: Is it the same for the bloom cycle?

Dan: We advise growers to drop the operating level to about four gallons per module during the fruit and flowering cycle. This helps ensure ample atmospheric oxygen uptake by the non submerged roots within the module. This oxygen exposure aids in proper fruit set and essential oil production as the plants mature. This technique can also mimic “drought conditions,” which triggers the plant to produce more oils as a means of reducing transpiration rates.

Everest: What about nutrient top-up?

Dan: The return module (epicenter) comes equipped with a high quality float valve built in for easy auto top-off. Each system also includes a bulkhead adapter for plumbing straight to your reservoir.

Everest: What about developing this set-up further with an auto-dosing system?

Dan: This system would work perfectly with an auto-doser like the Intellidose from AM. In this case you would plumb the Under Current (UC) float valve directly to a pure water source and let the Intellidose do the rest. Of course, you’ll need to set the doser to your specs, but then it’s on like Donkey Kong. The likelihood of a zero dump out run increases exponentially when a doser is used.

Everest: What EC should the top off res be balanced to?

Dan: When operated properly, top off should be balanced the same as the solution in the system. Traditionally hydro growers have been instructed to top off with half strength or pure water to avoid nutrient toxicity, but because the UC runs best with half strength nutes there is less of a chance of salt build-up. Ideally the solution in the system should stay balanced even as the plants use the nutrient and water. As a rule of thumb, if the nutrient EC/TDS rises as the solution is depleted you are likely running your levels too high to begin with. Conversely, if your EC/TDS drops it indicates you’ve started too low. Ultimately, as solution levels drop in the system the EC/TDS should stay stable; this is a good indicator that you’re dialed in. This EC/TDS stability will translate into improved plant health and greater pH stability to boot.

Everest: What if I experience drift in my nutes?

Dan: Correct it with your top off solutions. For example: a system started at 500ppm but has crept to 625ppm as the solution level has decreased. That’s a 25% increase, which can be easily offset by a top off res balanced at 25% below the initial 500ppm. This results in a top off res balanced at 375ppm to compensate. Ideally solution strength should stay constant as the plants consume it. This is a good indicator that minerals and water are being used at equal proportions.

Everest: What solution temperatures are optimal?

Dan: The system operates well anywhere from 65-80°F. We recommend maintaining a temperature between 68-72°F. This is a happy medium between optimum dissolved oxygen capacity and not chilling the nutrient solution so much that it slows the plant’s metabolism. If necessary, the water chiller can be easily adapted to the return pump.

Everest: Besides high water temps, what else can reduce dissolved oxygen levels in the system?

Dan: Elevated levels of dissolved solids can displace dissolved oxygen as they compete for real estate in the nutrient solution. So cool, half strength nutes are a perfect environment for high dissolved oxygen levels.

Everest: What dissolved oxygen levels should growers aim for in the UC?

Dan: We’ve tested on average +/- 9ppm of D.O. in solution. Water temps and quality will influence levels. As a point of reference, Dr. Elaine Ingham recommends no less than 6ppm to brew actively aerated teas.

Everest: You claim nutrient solution can last several weeks in the UC, but what about nutrient schedules that change by week?

Dan: Given that we encourage zero nutrient change outs, this does complicate things a bit. Best technique is to dilute any primary supplement into the top off reservoir.

Everest: How do you veg for the system?

Dan: Quad Tops are now available for the UC which allow up to four juvenile plants to be grown in each bucket. You can transplant our 5.5” heavy duty net pots right into your blooming UC rig. Other systems that veg well for the system include the GH Aeroflo2, AmHydro’s N.F.T., or transplant straight out of any aero cloner. Veg times in the UC are notoriously quick so start your fruiting cycles early to avoid overgrown madness. WE MEAN IT!

Everest: What grow media works best in the net pots?

Dan: Any non-wicking inert grow media tends to work best. Expanded clay pellets, growstones, silica stones, lava rock, sure to grow … to name a few. When using a wicking media like rockwool be sure to adjust the solution level to a point where it is not in contact with the media.

Everest: How much longer will nutrient stay viable vs. traditional ebb ‘n’ flow set-ups?

Dan: Time frames vary but typical change outs in E/F are about 7-10 days. In the UC, change outs should be necessary no sooner then 21-28 days. Many variables influence this time frame, so adjust your time frame to best meet your needs. Change nutes once they destabilize or become murky.

Everest: Is it a pain to clean in between crops?

Dan: Disassembly is not necessary. A bottle brush, green pad, biogreen and some elbow grease is all you need.

COOLING WITH WATER

Everest: Right, let’s talk about cooling this room with water. Many of our readers will be unfamiliar with using water chillers. Stephen, can you explain the basics of what a water chiller actually is and how it works?

Stephen: Sure thing. Firstly, water absorbs heat. And a water chiller cools water. So the basic idea is to use water to absorb heat from your indoor garden, and then a water chiller to get rid of it – similar to a regular air conditioner but with greater efficiency. A pump drives cool water through a manifold pipe and into a heat-exchanging device called an Icebox. The Icebox can be located on the exit duct of an air-cooled hood and provides increased surface area for the cool water to absorb heat from the hot air that passes over the grow lamps. The warm water then returns to the reservoir where it is re-chilled.

Everest: Why is water chilling more efficient than air conditioning?

Stephen: It’s down to the heat exchange capacity of water compared with air. The thermal conductivity of water is 23 times greater than that of air! A chiller will exchange the heat in a given space much more quickly than an air conditioner, allowing it to run less to get the same results. This is where you save electricity. With an air conditioner, air is passed over the evaporator instead of water. Since the air is less conductive, the evaporator can’t draw out as much heat as it can with water. The chiller evaporator is significantly smaller than an air evaporator because of the increased thermal load of water. In nearly all cases, the evaporator in a chiller will be significantly more efficient than that of an air conditioner, again allowing it to run less to get the same amount of cooling.

Everest: What type of chillers should be used?

Stephen: You need an industrial chiller – not a nutrient or aquarium chiller. Nutrient chillers might be more affordable, but they were not designed for battling against a constant source of heat! Only an industrial chiller is able to cope with constant loads and most can be placed outside if desired. Generally speaking, the larger your chiller, the more efficient it is.

Everest: How do you calculate the correct size of chiller for your room?

Stephen: Good question! Obviously this is really important to get right! First you need to decide whether you are going to use the water chiller simply for offsetting the heat generated by your grow lamps (i.e. keep your room at the same as the ambient temperature) or if you want to actively lower temperatures in your indoor garden further. It’s important to note that both heating and cooling are measured in BTUs (British Thermal Units). The first thing to do is measure how many BTUs are being generated from your equipment. In general, 1000 watt bulbs produce 4000 BTUs and 1000 watt digital ballasts produce around 2500s BTU of heat. (Exact figures vary.) That’s why ballasts should always be housed OUTSIDE of the garden.

Everest: So what sized chiller would this room need?

Stephen: 8 x 1000W lamps generate 32,000 BTUs. Each horse power of the chiller gives us around 12,000 BTUs. This room would need a 3HP chiller to cool the room entirely without A/C. Otherwise, a 3 ton A/C could be used in combination with a smaller (e.g. 2HP) chiller.

Everest: How is the cooling regulated / controlled?

Stephen: Cold water circulates around the system constantly. Regulation of the cooling effect is achieved through the fans that blow over the heat exchanger coils inside the Iceboxes. The fans are plugged into a thermostat controller. As it gets warmer, the fans speed up. As it gets colder, they slow down. The thermostat has a night and day setting.

Everest: Okay, now it’s time for the nitty gritty. I want to ask you about humidity. Surely cooling hot air rapidly through an Icebox creates condensation?

Stephen: A room full of transpiring plants is going to create humidity. Every indoor gardener has to deal with this and it’s easy to overcome with a dehumidier. As for condensation, the dew point changes with room temp and humidity levels. If you cool things down, water drops out of the air. Check out dew point calculators online. Typically, if you keep your humidity at below 50% then you will have no condensation.

Everest: How does the grower know how much the water needs to be chilled? I guess what I’m asking is, does the number of lights correlate to the water temp?

Stephen: Water temp is irrelevant to number of lights. You need to compare your water temperature with your room temperature. Assuming you have the right sized chiller, if the water temp is 10°F less than the room temp then you will maintain the room at that temperature. If you chill your water more than that it will create an A/C effect. 20°F difference will create active cooling in the room. It’s all about heat exchange and surface area, Everest, not just about how cold your water is. If you have three lights daisy-chained to just one Icebox, you can get the same results from three Iceboxes but you have to get your water a whole lot cooler. When you take away heat exchangers, you take away efficiency. But also, you need to take into account the volume of the room.

Everest: So you’re saying that a good rule of thumb is: the more Iceboxes (or heat exchange surface area), the better.

Stephen: You got it. The best efficiency is achieved when your water temperature is above the dew point and as close to your room temperature as possible.

Everest: Ok guys – that’ll do I think. I like the look of this room. Thanks for sharing!

What do you think of The Water Room? Have you used a similar set-up? Did Everest miss any questions? Post a comment below!

One of the most appealing aspects of hydroponics for any grower is the ability to recirculate water and nutrients.  Hydroponics can reduce water consumption by up to 80%!  Not to mention the financial savings to be made on nutrients and additives too.

However, recirculating nutrients brings with it additional challenges that the grower must meet in order to maintain maximum production.  So we asked Michael Christian, an expert consultant to the commercial hydroponics industry, to share his insights into recirculating nutrients effectively to achieve high performance plant growth while conserving water and nutrients.

The days of run-to-waste or open irrigation in horticultural operations are numbered.  Not only is pure water an essential resource that is becoming more and more precious as demand increases, but the minerals dissolved in water are also becoming increasingly scarce as they are mined from a finite resource, processed and distributed over long distances. We are quickly approaching the point where they must be recirculated in closed systems.

As food production becomes more localized, horticultural operations in controlled environments are being constructed in and near cities where food is grown short distances from consumers. Produce that is grown for freshness, nutritive value and purity is winning the day for people who care more and more about their health, their family’s health and where and who grows their food.

It is becoming more evident by the size and number of horticultural operations springing up all over the world, that hydroponics is the technique of choice. Why? Because it is not dependent on soil fertility and is therefore not limited by geographic location. Parking lots work well for hydroponic operations, as does hard pan soil and rooms inside buildings.

There are four basics elements of successful nutrient recirculation.  By “successful” I refer to the creation of optimum conditions in the root zone while still enjoying the efficiencies of maximum reuse of water and nutrients.

First, let’s state the common goals in any horticultural operation:

• Create and sustain an environment to generate healthy, vital, fully realized crops on a CONSISTENT basis.
• Avoid CROP LOSS at all costs. Crop loss can be defined as ANY condition or situation that detracts from our first goal. (Aiming for less than 10% crop loss is standard operating procedure in commercial operations.)

In addition, any successful hydroponic growing operation using a closed system (nutrient recirculation) must adhere to these fundamental basics:

• Pure water source
• Balanced nutrient ions/anions (CF)
• Optimum pH
• Plentiful oxygen availability
• Optimum light/temp/humidity/air circulation/CO2

Just to reiterate, if ANY one of these basics is out, plant performance will inevitably suffer.  It really is as simple as that. That’s why it’s important to understand each one individually and then how they operate in unison.  In this article, I’m going to focus on the first of these fundamentals.

To dial in any system is to get a handle on the variables and control them, period. Each one of the basics is a variable that must be managed… as any grower well knows, plant life has a way of beguiling even the most experienced growers. The better the understanding we have of each basic element, the faster we will be able to determine the one that is out and correct it with minimal drop in performance and / or recovery from crop loss.

Water is a universal solvent designed to carry minerals to the ocean and feed life forms on the way. It is hungry and will pick up any element it runs across and dissolve it in itself. It is guaranteed that the water that runs from your tap has a unique cocktail of minerals which may be fine to drink…but in a hydroponic system, it could be the kiss of death. You won’t know until you find out by analysis.

WATER

Water is the heart of a hydroponic system. If you don’t know what’s in your source water and you’re adding nutrients to it in a closed system, AND if plant performance suffers, you won’t have a clue if your water is the problem.  In addition, you will most likely spend a lot of time, money and effort taking ineffective actions to correct it.  This predicament is easy to avoid.  Simply obtain a water sample and get it analyzed. Actually, a simple analysis measuring the mg/l or ppm of, N,P, K, S, Ca, Mg, Cl, Na, Mn, Fe, B, Cu, Zn, Mb, Bicarbs, pH and EC in your water is all you need. If your plants require an EC of 2.0 and your source water is at .7 EC, you have only 1.3 EC “spare room” in which to add actual plant food. The rest is, who knows?  It’s what you don’t know that usually gets you.

All successful recirculating systems have plastic or stainless steel float valves… why? As water is transpired by plants, additional water is required to top up the tank.  Plants uptake more water than nutrients so if additional top-up water is not added to replace transpired water, the nutrient solution becomes more and more concentrated. Not a great situation if you are aiming for high performance. Large, fast growing, annual plants can drink up to a gallon of water a day especially when it’s hot. If it’s REALLY hot, plants will spend all their energy transpiring and NOT feeding which really adds to nutrient imbalance without a float valve.  So use the biggest reservoir you can handle AND a reliable float valve. (Remember that flood and drain systems will require the float valve to be installed at the drain level in the reservoir.)

With pure, low EC top-up water coming in through the float valve you’ll have no worries.  But if you have source water with a high or unknown EC you can be fairly confident that non-plant food minerals will start to accumulate.  This is because they are not being taken up by the plants. And unwanted or unknown nutrients take up valuable EC… in terms of chemistry, you can bet that there is mischief going on with the precious ion balance that you are trying to achieve with your spare no expense nutrients… plants will only tolerate this situation so long before plant performance suffers. So, TEST YOUR WATER… and avoid all that drama.

If you find your source water to have 40 ppm or more of Cl (chlorides from chlorine) you can off-gas it before adding to your tank or run through an activated charcoal filter. If Calcium and / or Magnesium are high and your water is hard then you will need to use a reverse osmosis (RO) system. Just be sure to run your water through a water softener pre-filter to take out the Ca so your RO membranes last longer. Check with you local garden/hydroponic store… if they are knowledgeable, they’ll have RO units and prefilters in stock. Determine how many gallons per day your plants will be transpiring (say 100) and size one with 25% greater capacity (125) than you need.

Go for a large volume reservoir. Rule of thumb… if you are growing 100 plants and, at their optimum size, they are transpiring half a gallon of water per day, or 50 gallons total, make sure your tank is ten times that (500 gallons). Why? Larger volumes of water stabilize temperature, help nutrient stay in balance longer, and enable the grower to make more subtle adjustments (top-up water added as well as nutrient and pH adjuster) to avoid any spikes in EC or pH that upset ion balance. A good rule of thumb for reservoirs – the bigger, the better.  We have growers with 12,000 plants in their systems running off of 1500 gallon reservoirs who dump their tanks every two or three months with no loss is crop performance. The water in their 1500 gallon reservoir will have been replaced completely with top-up water more than 12 times. This is what you want to aim for. These growers have pure, low EC source water, balanced nutrients, correct pH, large reservoirs, float valves and EC/pH dosers… the ingredients for successful, long term nutrient/water recirculation.

During the life of a plant, as it goes through vegetative growth, flowering and / or fruiting load, different nutrient ions are taken up at different rates. High Nitrogen (N), low Potassium (K) for vegetative growth, and low N, high K for fruiting / flowering growth. Rather than getting anal and freaky and adding all kinds of amendments and extra salts in anticipation of their shifting needs (and perhaps killing them with kindness), go easy! Large reservoirs have enough buffer built in and enough ions to take care of these phases without the balance shifting to detrimental levels and requiring frequent dumps. Particularly if you’re using a nutrient/pH doser (highly recommended), a well balanced nutrient added incrementally to a large volume of pure water will produce phenomenally healthy and robust plants all the way through flowering.

Continue with part 2, where Michael looks at nutrient balance and pH, how they work with pure source water, and how to manage them to steer plant performance.

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.

Join us as we take a peek inside your carbon filter to see what’s really going on!

Carbon filters contain activated carbon (also known as activated charcoal.)  Activated carbon is specially processed from charcoal at extremely high temperatures.  This process gives the carbon a very high level of “microporosity” or extremely fine porosity, visible only with the aid of a microscope.  When we refer to carbon as being “activated” or “active,” we are essentially referring to the existence of this “microporosity.”

To the naked eye, the contents of your carbon filter doesn’t look that exciting – just a pile of carbon granules.  The real magic of activated carbon only becomes clear when it is viewed under an electron microscope.  The key lies in its super-high surface area, visible as labyrinths of hills and gullies, perhaps only separated from each other by a few nanometers. Amazingly, just one ounce of activated carbon has a surface area in excess of 150,000 feet² (or about four football pitches.) These vast amounts of additional surface area created by these micro-textures dramatically increase the carbon’s ability to absorb molecules.

So how do you measure the efficiency of a carbon filter?  Well, it really depends on what you want to use it for.  Different types of activated carbon suit different applications.  Manufacturers of carbon filters sometimes refer to the ability of the activated carbon to hold iodine as a measure of its efficiency.  However, when using a carbon filter in a real indoor gardening scenario there is a lot more going on than in a lab testing for iodine absorption.

Airflow and Effectiveness

The big challenge for a carbon filter in an indoor growing scenario is the speed of the air-flow over the activated carbon. The activated carbon bed is being subjected to extremely high airflows with small contact times.  In fact, activated carbon industry experts are often astounded that the filters designed and used in indoor gardens are 100% efficient and operate for long periods of time.  Many growers use extraction fans to replace old air with fresh air in their indoor gardens.  This helps to insure sufficient levels of CO2 and keep the garden’s temperature and humidity within an acceptable range for healthy plant growth and bloom.  Often a carbon filter is inserted inline into the extraction system.  But many novice growers fail to realize how much extra resistance is created by their carbon filter – around 20%.  That means the CFMs of any extraction fan connected to a carbon filter are reduced by 20%!  (Not to mention the resistance caused by ducting.)  This is why it’s really important to over-spec your extraction equipment.

Key Quality Factors of Carbon Filters

• The actual surface area of activated carbon.
• The meso and micro pore surface of the carbon.
• The macro structure of the carbon particle.
• Packing.  Correctly packed carbon does not settle and allow air to pass through the filter untreated.
• How the above factors affect the airflow around each particle and ultimately through the carbon bed.

Filter Fact

Just like us, carbon filters gain significant weight during their lifetimes! The more weight gain the better. Highly effective filters can gain 12-15% of thir base weight. Low quality filters only gain 2-3 % weight.

Non-uniform carbon particle shapes and sizes create extra turbulence when air moves over them.  This contributes to increased entrapment of molecules.

To imagine this, picture some waves reaching a small beach.
Low turbulence = calm lapping waves.
High turbulence = huge crashing breakers on to rocky shore line.

Now try to imagine this within an airflow situation. Which scenario do you think works best?  It turns out that low turbulence is not what you’re after. The more the air swirls and gets pounded against the carbon the greater the removal of organic molecules. Smooth laminar airflow is not the aim of the game.

Humidity

Remember – carbon filters effectively stop working in very humid environments!  This is because water coats the activated carbon matrix, which simply means that no carbon surface is available to catch organic molecules.  Keep your garden’s relative humidity well below 82%.

Maintain the Pre-Filter

That white wrapping around your carbon filter isn’t just there to make it look pretty.  Dust and larger particles can physically block the activated carbon surface matrix.  The pre-filter is there to protect your carbon filter.  Never run your carbon filter without a pre-filter and make sure you wash it every three to four months.

Fly with the Eagles

The higher up you position your carbon filter, the more efficient it will be.  Warmer air will rise in your indoor garden.  It has more energy and therefore binds with more organic molecules.  You also want to be removing the warmest air from your garden in order to cool it most efficiently.

Depending on the filter / fan / humidity combination and the quality of the filter – they can be effective in an indoor garden for between eight months to two years.  Some stores offer carbon filter re-packing services.  Check with the manufacturer of your carbon filter to see if they recommend this.  Some carbon filters contain uniform pelletized carbon which is straightforward to refill whereas others are filled with a proprietary blend of particle sizes.

The optimum size for an activated carbon particle to remove volatile organic compounds from an airstream is 4.55mm to 6.55mm.  Smaller pieces tend to pack the filter bed causing “dead air passages” (blockages to the rest of us!)  These cause extra airflow pressure on the “live air passages.”

Believe it or not, the hobby hydroponics industry has created some of the most advanced designs in carbon air filtration and these cutting-edge techniques to remove organic molecules from high flow airstreams has since spread to other industries. However, the basic shape of the filter has not changed since 1985 – the cylindrical open mesh type canister, invented in Holland.  It is by far the most popular shape in use today. There is no more efficient use of materials and space to filter organic molecules from high flow airstreams.

Setting up a sealed indoor garden is more expensive but, if done correctly, it should give you the maximum ability to dictate and control temperatures, CO2 levels, humidity, and disease, 24 hours a day, 365 days a year.

Temperature

Now, some of you might be scratching your heads at this point. Isn’t a totally sealed room going to get really, really hot from all the grow lamps? And what’s going to stop the plants from suffocating to death, right? Well, these are the same challenges that face every indoor gardener. It’s just that the “sealed room” approach tackles these challenges in a different way.

First, let’s look at the whole issue of temperature. Every indoor gardener knows that it’s absolutely vital to control this key factor for successful cultivation. Plants perform better in optimum temperature ranges without large fluctuations. So how do we deal with all the heat produced when we fire up our grow lamps, dehumidifiers, pumps and ballasts? The answer is short and simple. AC, my friend! Air Conditioning is the only solution to beat the heat of a sealed room. Here’s an AC rule of thumb to help you spec the right unit:

You will need 4000 BTUs of cooling per 1000 Watts of lighting.

Example: 6 x 1000W= 6000 Total Watts of lighting  x 4000 BTUs= 24,000 BTUs of cooling required.

Note: the term “BTU,” or British Thermal Unit, is used to describe the power of heating and cooling systems. When used as a unit of power, BTU ‘per hour’ (BTU/h, that is, BTU divided by hour) is understood, though this is often abbreviated to just “BTU.”

Be aware that there are companies that have designed units specifically for hydroponic setups that can be installed without the expense of hiring in a certified electrician. These same units can handle the demands of constant cooling year around.

CO2

Next, let’s take a look at CO2 levels. We all know that plants need CO2 in order to photosynthesize, so we’re going to supply this if we’re not relying on fresh air ventilation. Growers using standard ventilation can maintain normal atmospheric levels of CO2 in their indoor gardens. If they wish to add more, however, they often encounter a dilemma. What’s the point of injecting extra CO2 into your indoor growing environment if it’s going to be vented out again before your plants have had a chance to benefit from it? Historically, growers have shut down their ventilation systems temporarily to give their plants time to absorb the extra CO2 but then, of course, temperatures begin to rise! It’s a bit like trying to fit a carpet that’s too big for the room!

With a sealed room you can inject optimum amounts of CO2 without worrying that it’s all being vented away. There are two standard ways to inject CO2 into your environment: using a burner, where natural gas or propane is lit as a flame and the off gas produces CO2; and bottled gas where you open a bottle of CO2, enriching the air directly. Using a burner is most common among larger setups of 6000 watts or more, due to the amount of CO2 required to drive PPMs from 400-2000PPM. This method can create additional heat due to the flame, but keep in mind that using AC can easily combat any heat issues you may have. There are also water-cooled CO2 generators on the market these days. The bottled CO2 is ideal for smaller rooms and can be equipped with diffusers that automatically release the CO2 gas as needed. Many growers have found that having CO2 enriched air in a grow room can produce up to 30% more yield.

Humidity

Next, let’s tackle humidity. Without venting moist air to the outdoors, the humidity in the indoor garden will quickly rise as the plants give off water vapor (transpiration). If humidity levels are too high it can be a cue for pathogens to attack and growth rates to slow dramatically. However, venting presents its own challenges. The outdoors will always dictate the humidity indoors as most places in North America have fairly high levels. In a sealed room you can control humidity to precisely where you want it, all day, every day, using dehumidifiers and air conditioners. Much like air conditioners, dehumidifiers are available in many sizes and properly selecting one for your size room is important. Lower humidity levels are often preferable towards the end of many plants’ flowering cycles to decrease the probability of mold and mildew.

Pests

Finally, a huge advantage of growing in a sealed room is disease and pest control. As long as you make sure you (the grower) stay clean, you can be sure that your environment is sealed from any nasty critters who see your plants as breakfast, lunch or dinner. To explain why a sealed room is ideal for disease control, ask yourself this question: how did my room get diseased in the first place? Much like humans, our environment means everything. It could be large temperature swings, high or low humidity, outside influences such as outdoor crop sprays, insects or anything else floating around. In a sealed room, you not only protect yourself from negative outside influences, but you also strive to create the environment you think is best – independent of what’s going on outdoors.

The sealed room concept has been successfully used for many years in gardens of all sizes.I hope that I’ve managed to inspire thoughts on how to bring a perfect environment to your garden!

Happy growing!

The cost of setting up an indoor garden can vary enormously. Basic set-ups can fall within most people’s budgets, whereas more advanced operations can see costs quickly mount up … and that’s without the addition of fancy control gear! So are these “smart boxes” really necessary for the hobbyist indoor grower or are they just for the pros – the control freaks? Jeff Broad, designer of the IntelliClimate, reveals all …

Control units are often regarded as a bit of a “luxury” for the lazy gardener. After all, you’ve shelled out all that dough for your lights, nutrients, additives, reflective material, extraction, ducting, pipes, gadgets and other gizmos. And then, as if all that stuff wasn’t expensive enough, there’s the little “box of tricks” winking at you from the corner of the grow store called the “control unit.”

Now, it’s true that many growers “get by” without using a control unit. So I guess the key question to ask is this: does the return outweigh the investment?

Environment is everything!

Talk to anybody who’s worked in a grow store for a few years. Most likely they’ve helped hundreds of growers diagnose plant problems. From limp stems, slow growth, and wilting leaves, to moldy flowers and stem rot – they’ve heard it all! And what’s the problem 90% of the time? ENVIRONMENT! It’s all too easy to blame it on this or that nutrient, or to seek a solution through some other “magical elixir,” but time and time again it’s the growing environment that’s at fault. So remember, when you grow indoors, bear in mind that you are the master of the environment. And depending on how well you do your all-important job, this can be a really good thing, or a really bad thing!

IntelliClimate being used in a greenhouse.

Still not convinced?  Well, take a fresh look at what’s inside your indoor garden! For one thing, those high pressure sodium lights belt out an incredible amount of heat – so that heat obviously needs to be dealt with (typically via an extraction system). But fixing one problem can create another, like trying to fit a carpet that’s too big for a room. We all know that if you want to enhance growth by using CO2 then having fans running all the time with the lights is not really going to work. All the injected CO2 will just get sucked out the window!

So what’s the solution? Well, one option is to spend all your time with your plants, constantly adjusting, tweaking, fine-tuning like a DJ on a pair of turntables, or … you can get real!

First, let’s kick off by taking a look at the critical factors we need to be mixing on our metaphorical environmental turntables …

Temperature and Humidity

These two factors are inextricably linked because for every 18o-degrees F (10o-degrees C) increase in temperature, the moisture-holding capacity of the air doubles (relative humidity halves). So the lights switch on and up goes the temperature – maybe by 18o-degrees F (10o-degrees C) or more – and the humidity plummets down to 40%, 30% or worse. Now, depending on the growth stage of the crop, this could be a disaster. For small plants with poorly developed roots, the humidity needs to be pretty high: around 80%. During vegetative growth: around 60-70%; and during flowering: around 40-60%.

With simple controls, you will find it difficult to achieve these levels as the lights will be heating and drying the air and so exhaust fans will be flat-out cooling and further drying the crop.

A humidifier may be used to help the situation and, with its help, you may be able to hold up the relative humidity at around 70%.

Now consider what happens when the lights are switched off.

Without the heat from the lights, the temperature falls by maybe 18o-degrees F (10o-degrees C)  and so the humidity will soar towards 100% with condensation occurring on the crop and other surfaces! Panic stations! We need to dehumidify before fungal disease sets in! So we set up a dehumidifier (also controlled by an automatic humidity controller. But wouldn’t it have been so much better if we could have anticipated the lights switching off and shut down the humidifier, say, 30 minutes earlier, leaving the crop nice and dry for night time? Ok, I hear you say, I’ll just buy another timer! Well you could, but the story doesn’t end here.

We really need to have a lower night temperature than day temperature – this is sometimes called “DIFF” and affects the crop’s tendency to stretch and grow vegetatively. To coincide with the lower night temperatures, we should ideally have a lower relative humidity. How do we achieve this? Two sets of thermostats and humidistats with yet more timers? This is all getting rather complicated. Maybe we should just forget about “DIFF” and hope for the best. Your friends get by okay, so why shouldn’t you, right? With a little luck we may get away with only a small reduction in yield, but if the weather gods are not with us things may not be quite so good.

CO2

Injecting CO2 into your indoor garden during the day period can significantly improve both growth and bloom. However, in practice it’s not quite as simple as that. The problem is that the garden needs to be kept closed so that the injected CO2 is not lost. If the only means of cooling is by extraction fans then we have a problem in keeping the room cool, so the first step is to use air-cooled lights. Although the glass causes a small reduction in light, the reduction in heating is many times greater and so they are definitely worthwhile. This is true whether using extraction fans or air-con for cooling.

Air-cooled lights are essential if you wish to inject CO2 unless you live in a very cold climate. Even with air-cooled lights, the temperature will rise due to the radiated heat. If extraction fans are used, cycling will be required.

The CO2 injection cycle

Inject!

In the first part of the cycle we have the INJECT state in which the fans are stopped and CO2 is injected either to a particular level as measured by a CO2 sensor or else for a fixed time calculated to fill the grow room to a specific CO2 concentration (usually 800 to 1,200 ppm).

Wait …

The next part of the cycle is the WAIT state which allows time for the crop to absorb the CO2 with the fans still stopped. This part of the cycle is the most difficult as it needs to be long enough for most of the CO2 to be absorbed but not so long that the grow room overheats. If you set it optimally one day, don’t be surprised if it is totally wrong for the following day when the weather is a bit warmer or cooler.

And Exhaust!

The final state is the EXHAUST state in which the extraction fans come on for sufficient time to completely replace the air in the grow room and cool everything down ready for the next cycle. This is normally kept as short as possible – just long enough to get the temperature and humidity down. Again, the time required will depend on weather. This simple system can work, especially in cooler weather, but in warmer weather the fans may need to be on all the time – in which case CO2 injection is not viable. A simple “cycle timer” may not “know” that the weather has warmed and may continue trying to inject CO2, either wasting it or overheating the crop. On the other hand, a smart controller will automatically adjust its targets to minimize CO2 wastage and, if this is not possible, will revert to external venting to bring in ambient CO2.

If you really want top growing conditions and wish to use CO2 enhancement during warmer weather, you really need an air conditioning unit. This will allow the indoor garden to be kept closed and make maximum use of the CO2 over extended periods. The split systems with a traditional thermostat (not the remote IR type) are generally the easiest to interface to grow room control systems.

But what if something goes horribly wrong?

Ok, let’s think of some Dr Pepper scenarios – like the failure of a cooling system or dehumidifier, or if CO2 fails, or if a power failure occurs. The system must respond as well, if not better, than if you were there flapping about it yourself. The control unit should try to maintain the best growing environment possible by trying alternative equipment to see if it can maintain environmental control (e.g. fans for cooling, air-con for dehumidifying, fans to bring in ambient CO2) and if this does not achieve the desired result it will need to take more drastic action like shutting down the lights one bank at a time. In the case of a power failure, we need to bring up the lights in an orderly fashion, first taking into account the minimum cool-down period, and then bring back each bank and each grow room in stages allowing the power surge from each bank to dissipate before switching on the next. With simple, discreet thermostats and timers this is not a simple task and the probability is that everything will come on together and trip the main circuit breaker.

You can probably see where I am heading. In my view, integration of the control equipment is essential. If you want to really keep on top of your growing environment there needs to be a ‘central brain’ controlling it all, not several disparate systems. No point injecting CO2 if the fans are on or are about to come on. No point humidifying if the night period is coming up shortly – we need to leave the crop as dry as possible. If CO2 enrichment is being used successfully then it is possible to allow the day temperatures to go a little higher. A smart, fully integrated system will know all these things and more. Some new controllers even allow you to set up a schedule of settings so that as time goes by, the settings automatically change. Take CO2 for example: young cuttings need very low CO2 as their roots are undeveloped, maybe 500ppm. Then, as they grow, the CO2 can be raised day-by-day up to the normal enriched point (800 to 1,200 ppm). At the same time, relative humidity is gradually decreased and temperature is raised. It saves a lot of time if all this is done automatically!

Control Unit Checklist

So maybe you’re convinced that buying a control unit is a worthy investment. What’s the next step? What should you be looking out for?

Reliability

Reliability is king! Luckily, modern electronics and the progression to surface-mounted components are providing a much higher level of reliability than in the past.

Adaptability

All growers’ requirements are different and if the controller cannot be adapted to suit differing climatic and indoor garden layouts then much unhappiness can result! As a designer of these units, however, I know it’s difficult to please everyone all of the time. For instance, you can include clever “self-learning features” which some growers will love and some will hate! While built-in intelligence is what it’s all about, it’s also important that you, the grower, feel ultimately in control.

Integration

From a functional point of view “integration” has also got to get a top ranking. Venting while injecting CO2 is no good for your wallet, never mind the planet. The interrelationship between temperature and humidity also benefits greatly from an integrated approach, especially when you add in some smarts to ensure plants are left dry for the night and the indoor garden is allowed to cool down prior to lights coming on.

Fail Safes

Check that any control system has good fail safes – things do go wrong and when they do you need to know that the system will respond to protect your plants. Also, check that the system will recover gracefully and systematically after a power outage.

Connectivity

Finally, computer interfacing is now available on some more advanced controllers. This heralds a whole new era of functionality and user friendliness. It allows the grower to schedule settings so that they automatically change as the crop matures. In addition, the computer connection allows remote access over the Internet or telephone line. Readings and settings can now be checked and altered without having to be physically present. Some garden controllers have the ability to send you a text message directly to your cell phone. From there you can log in, inspect any issues, and take appropriate action. Add a webcam and you can even visually inspect the area!

Installation tips

Install the control equipment outside the indoor garden if possible. This keeps it away from any possible high humidity and also allows you to inspect readings and settings without entering the grow room. It is great to be able to keep an eye on things during the night period without any risk of light entering and disturbing any photoperiod-dependent processes. It’s also useful to be able to access the controller when the CO2 is injecting; however, as all information is available on the PC this becomes less important.

The temperature/humidity/light sensor should ideally be located close to the growing tips of the plants so that it is measuring the same environment that the plants are actually experiencing. If it is positioned between light banks so that it picks up light from both, then it can be used to monitor both banks simultaneously. Some controllers do not have remote sensor boxes and so in these cases mount the controller and maybe a stir fan such that air from the growing canopy is directed toward the controller on a near-by wall. Do not be surprised to find that the readings in the growing canopy are significantly different to those on an adjacent wall.

So I hope that I’ve started your brain ticking and that I’ve shown you that being in control isn’t that freaky at all! In fact, it makes perfect sense and I know you’ll see a big difference in the quality and quantity of your crops. You may even wonder how you managed without one! Good luck and happy growing!

Jeff is the managing director of Autogrow Systems in New Zealand. He has over 20 years’ experience in the design of irrigation and environmental greenhouse control systems.  For more info visit his website: www.autogrow.com.

Just imagine that this super-experienced, righteous and magical dude has poked his friendly face around the corner of your indoor garden and, what’s more, he’s agreed to spend some quality time with you to get you growing like a pro. You see, Harmon was cultivating copious amounts of vegetables, fruits, flowers and herbs when Everest was no more than a spark in his daddy’s arc tube! Time to read and heed!

So pay attention, you soft and stroke-able newbie growers: here’s the Indoor Gardening Grand Wizard Harmon himself, ready to add some magic to your indoor garden!

#1 Environment is Everything

Greetings Urban Gardeners. Did you know that some new indoor gardeners think that all they need to do is buy a grow light and hang it above their plants? WRONG! These growers are underestimating the importance of environmental quality. Just like people, plants can only perform well when they are comfortable and receiving proper atmospheric conditions. Maintaining a proper temperature and humidity range is really critical to your success. Many plants enjoy higher relative humidity (60-80%) in their vegetative stage and lower (40-50%) during flowering. I try to maintain my indoor garden at 82°F (28°C) when the lights are on and 64°F (18°C) when they are off – but hey, that’s just me and my capsicums. Different plants have different requirements.

Equally important is clean air, proper CO2 / oxygen ratio, and adequate air circulation. You wouldn’t want to spend your life locked in a stagnant cupboard, would you? Air movement is your best defense against mold and other pathogens as well as the plants’ vehicle to remove waste products from the leaves and facilitate respiration. There is something magical about fresh air so don’t underestimate the importance of it. Fresh air brings fresh supplies of CO2 – a crucial component of photosynthesis – your plants can’t “breathe” without it! You can bring fresh air in with an intake port, exhaust fan and timer. Another way to ensure a constant supply of fresh air is to provide a convection air leak in the enclosure. Furnish a small hole near the floor at one end and another in the ceiling at the other end. Use some kind of filter to catch bugs and dirt. (At the very least a window screen or a pair of old tights if you have any spares knocking around!) For optimum control of temperature and humidity and coordination of CO2 enrichment and ventilation, specialized environmental controls are available to automate and maintain precise atmospheric conditions.

#2 Killing with Kindness

As your plants grow, their nutrient requirements increase, so it’s all too easy to get over-excited when they are young and err into over indulgence with fertilizers, plant additives, enhancers, and other stuff.  Sometimes it’s because of the old adage, “If a little is good, more must be better,” or you just follow too many people’s advice. Before you know it, you’ve got some kind of mysterious blend of chemical hocus-pocus that may not be compatible.

When you see curled leaves like claws, burnt leaf tips, slow overall growth or damaged new growth (terminal shoots), my advice is usually “go back to basics.” Flush the media with clean, pure water for a day or two, and then run a half strength dose of a good quality fertilizer. Once the plants re-establish themselves and begin to show normal growth, slowly increase the nutrient concentration and eventually you can start adding other growth enhancing products again.

A reasonable amount of additives can be very advantageous. My advice is to choose a well-established manufacturer who provides a complete line of nutrients and additives, and follow their program. Always use a conductivity meter to check the strength of your nutrient solution.

#3 Watering and Transplanting

Many new growers start with hand-watering their plants in soil and pots. It seems to be the simplest way but improper watering and transplanting is a common error. Start off your plants in small pots and make sure you transplant your plants in graduations. Let the plants develop a solid root ball before increasing container size, and then only step up a couple inches at a time. The theory here is to keep a consistent medium that the roots can dominate. Empty soil stays too wet and becomes water logged. The plant needs to generate a thick root ball mass to be healthy. Use a good quality soil mix that is light and provides good air retention. Pack the soil firmly and water immediately. Leave soil a few inches below the top of the container to hold water while it soaks in during watering. Do not water too often. It’s good to let the media dry out a little and then water completely. Feel the weight of the pot – it’s a great indicator of how much water is in the soil. Water lightly once to wet the substrate and break the soil tension, then come back after a minute and saturate. Let some water run out the bottom to leach out old contaminants. If you use trays under your pots, do not leave standing water. Kick the bucket, or lift it a bit to judge weight. This is a good indicator of water content. Too-frequent watering and over fertilizing is one of the most common mistakes new growers make. An old saying for soil growing is “fertilize weakly weekly,” and there is some truth to that.

#4 Understanding pH

Besides just the addition of fertilizer, nutrient solutions require other specific properties to work effectively. pH is an important factor. This ranges between 5 and 7 in most cases but varies depending on a gamut of particulars: cultivar, plant growth stage, type of grow system, fertilizer program, water characteristics, and even environmental conditions (light, heat, etc.) to name a few. My advice to growers is to let the pH run a range of about a full point. For typical plants, the rule of thumb is to aim for or 6.0 and let it rise (or drop as the case may be) about a point before adding adjusters. Essential elements become available at different pH values, so by letting your pH vary across the scale you have a better chance of all elements finding their optimum assimilation point. I prefer the range of 5.5 to 6.5 as a good gradient zone. Letting the pH drift alkaline (above 7.0) is more likely to stress plants than a slightly acidic pH. My main point here is that you don’t need to adjust your pH as often as you might be led to believe. Invest in a quality, digital pH meter and calibrate it regularly. Finally, only measure the pH of your nutrient solution once you have added all your fertilizer and additives, as these can affect it too.

#5 Nutrient Temperature

Root health is vital to your garden’s success so naturally you don’t want to cook your roots or allow them to become too cold. Nutrients are most easily absorbed when the nutrient solution is around 68°F (20°C).  Typically, temperatures in your indoor garden will drop at night as much as 10°F (5°C). That is perfectly acceptable. But if your water / nutrient solution is too cool it will cause the growth rate to decrease. Cold tap water can shock roots and cause other problems. However if the solution is too hot all kind of nasty things will happen. As water becomes warmer it can hold decreasing amounts of dissolved oxygen (which is really important for root health). If you are using a recirculating system, pay special attention to heat as it can transfer to the solution in many ways. The most common is absorption from trays, channels, containers or plumbing. This is a result of radiant heat from sunlight or even artificial lighting. Pumps can also create heat and be a factor. Protect your solution from direct sunlight. Insulate or sink your nutrient reservoir in the ground if possible. I have run my solutions through buried hose or pipe to cool them before returning to the system. Water chillers are available for extremely warm conditions. Nutrient heaters (with integrated thermostats) are also available at very reasonable prices to help you cope with cold conditions.

#6 Oxygen

Oxygen content in your nutrient solution is often neglected or misunderstood. Just like fish require oxygen in water, so do plants. Plant roots absorb O2 and need it for various purposes, but the primary reason for keeping an oxygenated solution is to fend off anaerobic bacteria such as Phytophthora root rot (blight) and damping off fungus (Rhizoctonia root rot). For the same reason, soil and other grow mediums must offer good aeration. As I said above, solutions can become depleted of oxygen if the water becomes too warm or stagnant. Organic solutions can easily become deficient as the culture often utilizes the oxygen. Dissolved oxygen is measured in mg/L. Typical optimum values range about 10 and 30 mg/L. Over 40 is considered saturated and under 5 is considered deficient. There are reagent kits and meters available but I hardly find them necessary. Air stones or spray nozzles generally do the trick. I often use a hose-end siphoning device designed for proportioning liquids into a hose stream and just let the intake suck air. It will induce fine bubbles into your water flow. They are cheap and widely available in garden shops. Soils should contain good porous substrates and, again, be sure to let them dry out between watering. Finally, keep your nutrient solutions agitated to prevent stagnation.

#7 Lighting

You could write a whole book on lighting an indoor garden so I’ll just try and outline some basic principles here. Where you place your lights can dramatically influence plant growth rate and structure. If the light levels are insufficient, plants will respond slowly and tend to be weak and elongated. It will be fairly obvious; you need more light. If the lights are too close to the plants the new growth will dry and curl. This will also be pretty apparent and is a more common mistake. Place your hand at the same level as the tops of your plants. Keep it there for a minute or so. If your hand starts to become noticeably warm your lights may be too close. Another good way to measure temperature is to fill a small plastic bottle with water and hang it at plant level with a mercury thermometer in it. This will provide an accurate interpretation of actual temperature. Most of the heat accumulation in an enclosure is from the lights. Air and water-cooled fixtures are a very effective method to remove unwanted heat before it becomes an atmospheric concern.

#8 Know Your Limits

Many plants have a vegetative stage and a flowering stage. Basically, the vegetative stage is when the plant builds its structure – the botanical ‘scaffolding’ to support the future harvest. The flowering stage is when the plant stops growing and focuses its energies on producing flowers and fruit.

What makes a plant flower? Many things can trigger it, depending on the plant type. For instance, I delay my capsicums from producing fruit by physically picking off the flowers. I do this so that they first grow to a decent size before concentrating on producing a bigger harvest for me!

Plants like Poinsettia and Kalanchoe require short day lengths in order to start flowering (usually 11 hours or less). In an indoor garden, you can control when these plants grow and flower just by changing the length of your lights-on period. If you’re growing plants like these (known as ‘photosensitive’ plants) it’s important to ensure that they enjoy complete darkness during the lights off period – so no peaking! They require uninterrupted darkness in order to properly trigger flowering.

I’m wary of opening up a can of worms here but consider the following simple advice:  When growing plants indoors, it’s important to take the space you have available into account. Sounds like commonsense, huh? But listen! It’s all too easy to get carried away in the vegetative stage, thinking that the bigger you grow your plants, they will automatically carry more fruit. This is true to an extent but you have to match the size of your plants to the containers they are grown in, the space available in your indoor garden, and the amount of light available. Also, remember that the transition from vegetative into flowering can be fairly gradual (it doesn’t happen overnight!) so growth can continue for a while even after you induce flowering with shortened days / lengthened nights. Knowing when to induce your plants to flower is a fine art (or science, depending on how you look at it!). Novice growers invariably grow their plants way, way too big at first.

#9 Don’t Get Bugged Out

Keep your indoor garden clean. Don’t get lazy: otherwise insects and diseases will be on you before you know it! Insect and disease control is one of the most devastating and misunderstood hazards of hobby growers. You get bugs, or at least finally notice them, and at that point it is often too late. You spray for them any number of lethal or ineffective insecticides, and that seems to help, but it takes a toll on your plants, and then the bugs come back. It is frustrating and it can cost you your yields and all the time and money you have invested in your garden. Plant diseases are much the same story. But there is a rhyme and reason to this dilemma. You just need to learn the timing and lifecycles of these ailments. You need to be proactive. Take precautionary steps. Beat them to the punch. There are many methods to avoid infestation, both procedural and environmental.

Clean the grow area and all plant equipment and systems between crops. Use 10% sodium hypochlorite (household bleach) or 3% hydrogen peroxide or whatever your desired disinfectant might be. Clean and rinse well. This is the best way to avoid common plant disease. Use filters to keep outside bugs and spores out.

Healthy plants are reasonably capable of fending off disease by their own mechanisms, whereas stressed plants become susceptible to all pests and disease. Bugs and disease usually start on one plant. Closely inspect all plants frequently, especially ones which seem to be weak or ailing. Learn where they hide and the telltale signs of damage. If you find a bug, act quick to reference information on the remedy. Bugs (and disease) have very definite life cycles. Don’t just spray, do your research. You have to know what, when, and how often to administer treatment. There will be a pattern of applications necessary to stop the infestation. This is the key. Believe me. You’ve got to be smarter than the bug (and that takes some effort!), but you will thank yourself many times over if you learn the fundamentals of proper insect management. Otherwise forget it. You might as well give up now and save yourself all the frustration of failure. Once you have a clean garden you might look into the application of predatory bugs, however this takes a wholly different level of skill and knowledge. There is so much more I want to tell you about this subject but … they don’t pay me enough for that. Heheh.

#10 Be Observant!

One of the most common mistakes, if you can call it that, is just not paying attention. You need to spend time just looking closely at your plants. Get your nose dirty. Become one with them. You can actually learn to feel what they feel. And in doing so, you can share in their triumph and trauma. Don’t be afraid to touch the plant. They like it. A healthy plant is not frail. Feel its structure and feel its life force. Look closely at your stem and sun leaves. Look for bugs or mold, injuries or deformities. Look under the leaves and on top and in the internodes. Look everyday at the new growth, the apical meristems and terminal shoots. Look for dry or curled tips, chlorosis or darkening of the stems. They should be growing constantly and look lush and bright green. Rejoice in the splendor of the tiny new leaves unfolding. Use a magnifying glass or microscope at times. Get into it. There is a lot to be learned and gained by simply being observant.

Good luck and happy growing.

Harmon Davidson
Green Air Products