Michael Straumietis, founder and owner of the only hydroponics nutrients company that designs and tests its products on cannabis, remembers when he visited a 20-light grow op that had inadequate air conditioning.
“They needed 6000 BTUS of cooling power for every 1000-watt light, but they had half that,” he says. “The grow room temperatures were in the high 90s when the lights were on. The plants were barely alive, and the growers were going through hundreds of gallons of water and many bottles of nutrients because the plants were so thirsty.”
Marijuana grow room temperatures affect the health, growth rate, size, bud quality, and yield of your cannabis plants, Straumietis explains..
“Controlling grow room temperatures, and the temperatures themselves, affect how much money you spend on your indoor grow op, how well your hydroponics equipment performs, and how healthy and productive your plants are,” he says.
As with many marijuana growing issues, the ideal temperature for your grow op is variable, depending on several independent or interlinked factors.
One important factor is the gap between lights-on and lights-off temperatures.
Especially in bloom phase, you want your lights-off temps to be about 7-10 degrees cooler than your lights-on temps.
This promotes resin production, purpling, and bud growth—while decreasing the vertical stretch that usually comes in the first weeks of bloom phase.
Having a sufficient gap between lights-on and lights-off temperatures is especially important for marijuana strains with genetics native to Afghanistan and other areas where nighttime temperatures are much colder than daytime temperatures.
Another big factor for marijuana grow room temperatures: are you using carbon dioxide (C02) or not?
If you’re using C02, your marijuana grow room temperatures can be as high as 85 degrees Fahrenheit, which is 10-11 degrees higher than ideal lights-on temperature in a grow room where you’re not using C02.
Yet another factor is: what type of marijuana growing are you doing?
If you’re using pure or media-based hydroponics including deep water culture (DWC), aeroponics, NFT, rockwool, coco coir, grow rocks or coco coir, your nutrients water temperature is a crucial factor in your marijuana grow room temperature.
Marijuana root zone temperature should be around 67-68 degrees Fahrenheit, and that’s why many growers use a chiller to keep their hydroponics water in that range.
When your hydro water temp is 67-68F, it offsets hot marijuana grow room temperatures to lower the stress your marijuana plants experience from hot grow rooms.
Yet another factor for marijuana grow room temperatures is: what strains of marijuana are you growing?
Sativa-heavy cannabis strains, especially those with tropical genetics such as Haze varietals, like warmer marijuana grow room temperatures in the range of 76-81 degrees Fahrenheit.
Indica and Afghanica dominant marijuana strains, especially those with genetics that come from the Himalayas, Northern India, Afghanistan, Canada, Holland, and other cooler climates, do best in 73-74 degrees Fahrenheit grow rooms.
Purple strains do way better with cooler temperatures during lights-off in bloom phase.
Excessively-hot marijuana grow room temperatures create plant stretch, plant stress, fluffy buds, and increased pest and disease problems.
Also realize that marijuana grow room temperatures that are too cold (below 70 degrees Fahrenheit) may slow plant growth and decrease yield.
Lights-on temperatures below 65 degrees Fahrenheit in your marijuana root zone may deter root function and harm roots.
Lights-off root zone temperatures below 63 degrees Fahrenheit aren’t good for marijuana roots either.
“That’s why it’s not a good idea if you’re growing in a cold climate or a basement to put your plants directly onto the floor or concrete. It can make the roots too cold and that definitely slows growth and can create root pathogen problems,” Straumietis says.
Occasionally, growers have to use aquarium water heaters to keep their nutrients water warm enough.
Everything depends on your particular marijuana grow room temperatures situation.
Note that grow room relative humidity should be between 55-64%, and that non-optimized marijuana grow room temperatures combined with the wrong humidity creates many problems for marijuana plants.
Achieving the right marijuana grow room temperatures and humidity involve air conditioning, venting, air exchange, and dehumidification.
Take a look at this article on hydroponics grow room monitors and controllers. These devices make it easier for you to control marijuana grow room temperatures and other environmental factors that affect the health, potency, operating costs, and yield of your marijuana plants.
Also look at this article that explains how to combat excessive heat in marijuana grow rooms.
“You give your plants the perfect temperatures and humidity I’m talking about, and feed them Advanced Nutrients and lots of light in the right spectrums, and you’ll immediately see heavier harvests of more potent buds,” Straumietis says.