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.

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

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

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

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

Included accessories

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

Setup & Installation

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

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

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

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

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

Operation

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

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

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

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

Performance

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

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

Heat

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

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

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

Safety

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

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

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

How to make it better?

For once, I’m stumped.

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

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

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

Conclusion

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

Simple. Cool. Efficient. Safe. Enough said.

Happy Gardening,

Curtis

Unless you want to sit in front of your plants and breathe sweet nothings onto your plants, you need to artificially add CO2.  Indoor gardens love a carbon dioxide concentration of 1500 PPM.

Under the rarest of occurrences, you can boost that to 10,000 PPM for 15 minutes to kill all crawling critters molesting your plants.  Be careful with this application and know thoroughly what you are doing.  Such high CO2 concentrations will kill you.

There are currently two ways to add CO2 to an environment:
1)  Get a CO2 tank and CO2 regulator to maintain a consistent PPM.
2)  Use a CO2 generator to burn propane and separate the CO2 from the propane with the assistance of an electric monitor or regulator to control the on/off of the CO2 generator.

Hydro Innovations’ CO2 Monitor fits the bill.

The CO2 Monitor is a perfect example of KISS (Keep It Simple, Stupid).  Plug in the monitor, connect your choice of CO2 generators, wait a few seconds for the monitor to boot up, and you’re ready to roll.  I would recommend placing the monitor at the opposite corner from your generator to ensure a minimum application of CO2 to all corners of your grow room.

The monitor defaults to maintaining the environment at 1500 PPM of CO2.  It starts your CO2 generator at 1300 PPM and shuts it off at 1500 PPM.
Here we have what’s included in the package.
– 1 A/C adapter for the CO2 Monitor itself
– CO2 Monitor with power cable for your CO2 generator

You can mount the monitor to the wall for easy reading.  For myself, I set the CO2 Monitor down in a corner of my grow room, opposite my CO2 generator.

I have the CO2 Monitor connected to the same timer as my grow light.  Plants don’t really require much CO2 during lights-out, so any generated with the lights out is a waste.

Fancier CO2 Monitors (read:  more expensive) can fine-tune the PPMs in your grow room.  Really, you don’t have to.  KISS is good for you.  On at 1300.  Off at 1500.  Easy.

My only suggestion for improvement to the monitor is to incorporate its own power supply into the plug, which also powers the generator.  However, this would require some tricky electrical engineering to power the monitor and not power your CO2 generator. This would eliminate the extra AC cable.

Simple partner for your CO2 generator. Get it. Connect it. And forget about it.

Happy Gardening!
Curtis

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

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.

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!

Dan’s Method – Calculating By Room Volume

You will find many calculations on the web for sizing a fan for ventilating indoor gardens; however, what many of these calculations fail to take into consideration is the friction loss on carbon filters and increased temperatures from HID lights. So here’s my calculation method, which you can use as a guide for sizing an exhaust fan for a growing area. Keep in mind that this calculation will give you the lowest required CFM (Cubic feet of air per minute) required to ventilate the indoor garden.

Step 1 – Room Volume

First the volume of the room needs to be calculated. To calculate, multiply length x width x height of growing area. For example: a room that is 8′ x 8′ x 8′ will have a volume of 512 cubic feet.

Step 2 – CFM Required

Your extraction fan should be able to adequately exchange the air in an indoor garden once every three minutes. Therefore, 512 cubic feet / 3 minutes = 171 CFM. This will be the absolute minimum CFM for exchanging the air in an indoor garden.

Step 3 – Additional factors

Unfortunately, the minimum CFM needed to ventilate a indoor garden is never quite that simple. Once the grower has calculated the minimum CFM required for their indoor garden the following additional factors need to be considered:

• Number of HID lights: add 5% per air-cooled light or 10-15% per non-air cooled light.
• CO2: add 5% for rooms with CO2 enrichment
• Filters: if a carbon filter is to be used with the exhaust system then add 20%
• Ambient temperature for hot climates (such as Southern California) add 25%; for hot and humid climates (such as Florida) add up to 40%.

An Example

In our 8’ x 8’ room we have 2 x 1000w air cooled lights, and we plan to use a carbon filter. We also plan to use CO2 in this room. The ambient temperature is 90 °F (32 °C), however, we will be using air from another room that is air-conditioned. Here’s the minimum required CFM to ventilate the room:

1)    Calculate the CFM required for room (see above).
2)    Add 10% (for 2 air cooled lights).
3)    Add 5% of original CFM calculation (for CO2).
4)    Add 20% of original CFM calculation for the carbon filter.
5)    Air is coming from an air-conditioned room so no need to add any other percentages.
6)    CFM = (171CFM) + (171CFM x 10%) + 
(171CFM x 5%) + (171CFM x 20%) + ( 0 )
= 231CFM.

This is the absolute minimum CFM required to ventilate your room.

The next step might seem to match the closest fan to this CFM. However, for this example I’d choose a six inch fan with a CFM of around 400 or more, and a 6 inch carbon filter to match. The extra CFMs may seem a bit excessive (calculations on most indoor gardening websites would recommend a 4” fan and a 4” carbon filter) but it’s always better to over-spec since we need to compensate for air resistance in ducting too.

Also, as we are using a carbon filter we will need to match the fan with the filter so that the fan that will neatly fit onto the filter.

Note: If all the variables are kept the same and we changed the room size from 8’ x 8’ to a 12’ x 12’, then the minimum required CFM would be 519 CFM.

The All-Important Inflow!

An intake port can be anything from a gap under the door to an open window – even a hole in the wall. The best place for an intake port is diagonally opposite from your exhaust fan; that way, air has to pass across the entire room – very efficient. You can put a piece of screen over the opening to keep insects and animals out, a piece of A/C filter to keep dust out, or a louvered shutter or backdraft damper that opens when the fan turns on and closes when it turns off. You can also use a motorized damper. This gets installed in-line with your ducting and is plugged into whatever device controls your exhaust fan. When your fan turns on, it allows air to pass. When your fan shuts off, it seals completely, preventing CO2, air, etc. from passing. You can get creative with these devices and use one fan to control two rooms, etc.

One additional note about intake ports: you will see much better results from your exhaust system if you install a second fan to create an active (as opposed to passive) intake system. Normally, when your exhaust fan sucks air out of your room, air is passively going to get sucked back into the room. By installing a second fan on the intake side, you will reduce the amount of negative pressure created in the indoor garden, thereby cutting down greatly on the amount of work the exhaust fan has to do and allowing much more air to pass through. If you’re not sure or you don’t want to spend the money, start out with just an exhaust fan. If it’s not performing as well as you thought it would, try adding an intake fan – you’ll smile when you see the difference!

Fred’s Method – Calculating By Wattage

Hello there. First off, I’m used to working with Celsius, not Fahrenheit, but I’ve done my best to provide formulas for both. My method for calculating fan requirements does not cover active cooling with air conditioning systems or cool-tube designs. We’re talking about everyday grow chambers here, totally enclosed for air-flow control, with no large amounts of radiant heat into or out of the box. Your mileage may vary some for these reasons.

Right then, let’s get started:

1) Start at the beginning and design this right! Before you even buy or cut anything for your new project, determine the highest temperature that your intake air will ever be when lights run. Call this T (inlet).

2) Use these formulas to determine the difference in temperature you can tolerate. 80 °F (27 °C) is just about the optimal for growing most plants. You can go up to 76 °F (30°C) if you have to, but aim for 80 °F (27 °C).

Tdiff = 27 °C – T (temperature of inlet air)

3) Add up wattage for all power sources in your indoor garden. Lights, pumps, heaters, humidifier, radio, coffee maker, whatever! Add it ALL up and call it Watts. If it is on for more than three minutes and uses more than a watt, add it up. This will make your number worst-case and therefore a conservative value.

4) Compute the absolute minimum fan power you will need using the following formulas. Fan power is measured in the amount of air (cubic feet) shifted per minute. The formula below is the minimum fan rating you must have to achieve your temperature goals. You will have to increase fan power to compensate for duct constriction, small inlets, carbon scrubbers, screens, or other items that block airflow.

CFM = 1.75 x Watts / Tdiff (in Celsius)

If you prefer to work in Fahrenheit, try this formula:

CFM = 3 x Watts / Tdiff (in Fahrenheit)

5) Get at least this fan power or don’t come and ask questions! If you are going to have more than one fan, they should be mounted side-by-side rather than inline if you want to add their different CFM ratings. For inline fans, use the lowest air-flow rating of all fans in the path. A fan on the inlet and a fan on the exhaust of the box are considered inline fans. Fans just circulating air inside the indoor garden should not be counted for airflow but must be included in your initial wattage calculations.

Ok, to see these formulas in action we’re going to have to do a little number crunching:

An Example

Ok, let’s say you have 2000 watts in a 8 foot by 8 foot room with an 8 foot ceiling height.

So what amount of air do I need to move to keep the room at 82°F (28°C)? My incoming air temperatures are 68°F (20°C) during the lights on period.

Tdiff = 28 – 20 = 8°C

For Celsius the formula comes out at:

CFM = 1.75 x 2000 / 8 = 438 CFM

For Fahrenheit we get the following:

Tdiff = 82 – 68 = 14°F

CFM = 3 x 2000 / 14 = 429 CFM

Here’s a quick look-up chart to show some further examples:

Remember, Tdiff shows how much your temperatures will rise above your inflow air temperature for a given wattage and air movement.

* Just a humorous example. 1000 watts of light with a PC computer fan (15 CFM) – temperatures rise 189°F according to this formula!

If you are adding any carbon scrubbers or extensive ductwork, this is where you add to the fan size to account for air pressure losses. You have to move this many CFM, or the numbers don’t come out right.  Exactly how much these items diminish your airflow depends on your exact configuration and is beyond the scope of this introductory article!

What to do when your outside temperatures are higher than your maximum allowed indoor garden temperatures:

You have a few choices:

1)    Stop growing for a while ’til things cool off, or try running your grow lamps at night when inlet air will be cooler.

2)    Reduce your lighting to drop the heat load. Not good if the incoming air is already over critical when it arrives in the box. Might be possible if the inlet air temperature is lower but you are running too many lights to keep up with the cooling.

3)    Use active air conditioning.

Any other helpful formulas out there? Tell us about it below!

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