Excess heat in your grow room really sucks. Not only does it place extra transpirational pressure on your plants, but it can seriously degrade the quality of your final product. This is particularly relevant to growers specializing in aromatic / culinary herbs where essential oil production is key to the development of good flavors and aromas. Also, if you are growing plants that enjoy cooler conditions (e.g. cold season crops like lettuce or cilantro) or species native to higher altitudes then heat problems are top of your avoid-list.
But here's the deal. Grow lights—while amazing at producing the intensity and quality of light necessary for strong and healthy plant growth—also produce a whole lot of heat. If you don't deal with this heat using ventilation or air conditioning, then temperatures will quickly rise into the 80s, 90s, and even beyond.
Commonly, indoor gardeners shoot for somewhere in the 70s during the day and the 60s during the night. Use a min / max hygrometer / thermometer to measure relative humidity and temperatures in your garden. You should get into the habit of resetting it every day so that you can see the peaks and troughs over the last 24 hour period.
If your grow room is 80 or above—and you're not supplementing with additional carbon dixoide—then my bet is your indoor garden is too hot. Sure, your plants won't die but the quality of your harvest will definitely be hit. Cuttings from the same mother plant, grown in different conditions will look, smell and taste like very different plants.
10 Tips to Beat Heat in Your Indoor Garden
Check out these ten ways to combat heat issues in your grow room.
Combat Heat Issues in Your Indoor Garden in 10 Ways!
#1: Increase air exchange. Crank up your input and extraction fans to bring more cool, fresh air in, and remove more hot, stale air from your garden. A thermostatically controlled fan speed controller will do this for you automatically, instead of you having to manually turn dials. Check out the Kronus series by Titan Controls or the Zephyr One. Also, be sure to take your input air from the coolest place you have available. Some growers use an air conditioner to cool their input air, especially during the summer.
#2: Lower nutrient strength. It’s hot so your plants are taking up more water, but that, in turn, forces them to take up more nutrients. This can cause toxicity issues. Diluting your nutrient solution by 20% with pure water is a real stress buster. Keep it well agitated with an air-pump and air-stone too.
#3: Increase air movement Use oscillating fans to move the air within your grow room, especially the air in between your lights and the plant canopy.
#4: Increase humidity If your relative humidity has dropped below sixty percent and your plants are in vegetative mode, or below forty percent when in flower, switching on a humidifer will have a cooling effect on your plants.
#5: Dim your lights or switch some off! Raising your lights won’t remove heat from your room. Try switching off half of your grow lights, or use the dimming function on your e-ballast, if you have one—especially effective with HPS lamps. Better to simulate a cloudy day than a scorcher.
#6: Chill your nutrients Plants can tolerate really high air temperatures, 90, 100 Fahrenheit or more, IF the nutrients are chilled to around 66. Growers will use a pump to circulate their nutrient solution through an aquarium chiller.
#7: Use Air-Cooled Reflectors Air-cooled hoods, such as the Magnum XXXL or Blockbuster, allow growers to remove up to fifty percent of the heat generated by the lamp before it even enters their garden. Use insulated ducting to increase efficiency. Check out my other video on setting up air-cooled hoods the right way.
#8: Run your lights at night This may sound obvious but I don’t want to leave it out. If you’re flowering short-day plants that only want 12 hours of light a day, run your lights during the night. Not only may the electricity be cheaper, but your ambient temperatures will be lower when your lights are on, making your life easier.
#9: Seal it up! Ventilating an indoor garden doesn’t work for all growers—especially those in hot climates. Typically these growers seal their grow rooms, cool with an air conditioner, and add carbon dioxide using a generator or a tank connected to a regulator. It’s also worth noting that plants can tolerate higher temperatures in conditions with elevated CO2—up to thirteen-hundred PPMs, about four times normal atmospheric levels.
#10: Nutrient additives and beneficials Increased silica will help your plants solider through a hot spell by toughening up cell walls. Check out Armor-Si (armor see) from General Hydroponics, an awesome silica supplement. Sub-Culture M and Sub-Culture B, also by General Hydroponics, will help to colonize your plants’ root zones with beneficial bacteria and fungi, making it harder for pathogenic organisms to get a foothold. Failing all that—move your garden to a better insulated location—preferably under the ground where you can benefit form natural insulation. Finally, remember that temperature control is particularly important if you’re ripening flowering or fruiting annuals that are expecting cooler fall conditions.