Temperature Humidity and C02




It's Getting Hot in Here...

Plants don't wear clothes. They're already naked. So what can indoor gardeners do when temperatures in their growrooms gets too high? Everest Fernandez comes up with some obvious and not so obvious suggestions for countering high temperatures in your indoor garden.

aaasun.svgSummer is coming - in the northern hemisphere anyway! And higher temperatures outdoors can often spell problems in your indoor garden. So, other than shutting down and waiting for cooler months, what can indoor gardeners do to counteract excessive heat problems in their grow rooms?

1) Run Things at night.

I know I'm going to get a lot of flack for stating the obvious here but here goes anyway. Ambient temperatures are cooler at night so it makes sense to run your grow lights during nature's lights-out period. This has a knock-on benefit too. It'll be easier to maintain warmer temperatures during your plants' dark period if your lights are off during the day. A lower difference between your lights on and lights off temperatures (known as tdiff) often leads to squatter, less leggy plants which are typically easier to grow efficiently under artificial grow lights.

2) Change Rooms.

Ideally your grow room should reside within a well insulated room with no external walls facing the sun. Basements are ideal, although you should keep an eye on relative humidity issues when growing underground. However, the absolute worst kind of rooms to be growing in during the warmer months are poorly insulated, sun-facing rooms, especially in wooden houses or new-build pre-fabricated homes.

3) Use a White-Lined Grow Tent.

Did you know that silver-lined grow tents are typically 6 - 8 °F hotter than white lined grow tents? That's because the silver acts as a better insulator. So why isn't everybody growing in them? Well, here's a little history for those who need it. White-lined grow tents have an undeserved bad reputation—especially in North America. Back in the early days of grow tents, a less scrupulous manufacturer created a series of cheap tents with low grade materials that off-gassed harmful toxins into the growing environment. The result was yellow plants and very, very unhappy growers. The material to blame was a low-grade PVC used as an inner-layer to provide light-proofing. The reflective layer of these off-gassing tents just happened to be white. So growers and retailers made the 2+2=5 arithmetic that all white-lined grow tents were bad for plants!

White vs. Silver

Watch this video comparing silver and white lined grow tents.




If you use grow tents in a hot area, you should definitely consider switching to a white-lined grow tent. The creators of the original grow tent, HOMEbox have just released a PAR optimized grow tent range called PAR+.

4)  Reduce Nutrient Concentration
Highly recommended for hydroponic growers! This is a tried and tested commercial technique. In hot conditions your plants are transpiring more moisture than normal. This means that your plants are using a higher water : nutrient ratio. The net effect is a concentration of your nutrient solution which then places cumulative stresses on your plants. Try reducing the concentration of your nutrient solution by 25%. (E.g. If you are running an E.C. of 2.0 (~1400 PPM) try reducing it to 1.5 (~1050 PPM) in hot conditions.)

5)  Temporarily raise your Grow Lights
By positioning your grow lights further away from your plants, (an additional 6 - 12 inches) the canopy will be exposed to less radiant heat emitted from the lamp. Of course, if your grow lights are too far form your plants for a prolonged period of time your plants will inevitably begin to stretch in reaction to insufficient light levels, but this is a good strategy for a heat wave lasting just a few days.

6)  Dim your Grow Lights
Some models of electronic ballasts now carry a dimming or dial-a-watt feature affording growers the option of running their HID grow lights at 75% or 50% full power and thus, producing less heat. Growers should note that the spectral distribution of some lamps (particularly metal halides) can change in dimming mode (i.e. some parts of the spectrum dim more than others.) Dimming is not recommended for metal halide lamps. Raise your lights instead!

7) Power Down!
It's much, much more preferable to simulate a cloudy, overcast day than a scorched desert. Don't be afraid to switch off half of your grow lights for a few days during a heat wave.

8) Add Air Conditioning
An A/C unit is the ultimate way to control temperatures in your indoor garden. Reasonably priced, portable, self-install units are available. Otherwise, if you're using standard ventilation to cool your room, take your inputs from the coolest place you can and run your fans 24/7.

9) Keep Your Roots Cool
The optimum temperature for active metabolism in most plants' root zones is around 64-68°F (18-20°C). Ensure that your water or nutrient solution is at this temperature too. If using tap water, be sure to add just enough from the warm tap so that the water feels tepid-not warm, not cold, just silky to the touch. Better yet, invest in a nutrient thermometer or a thermostatically controlled nutrient heater.

10) Invest in Air-cooled reflectors /hoods
Air cooled reflectors, when used right, can really help to keep a lid on temperatures in your indoor garden. Use a dedicated inflow for the input air and duct the output air straight out of your grow room using insulated ducting. You should always keep ballasts out of your garden as they put out a lot of heat too!