Grow Room Enviroment

Are You A Control Freak?

Are You A Control Freak?

The cost of setting up an indoor garden can vary enormously. Basic set-ups can fall within most people’s

Are You A Control Freak?

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

IntelliClimate being used in a greenhouse
IntelliClimate being used in a greenhouse

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.


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


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!

Are You A Control Freak?

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


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.


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.


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.  


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