What’s the Best Temperature for Growing Marijuana Indoors? To answer the question, STUFF STONERS LIKE have teamed-up with expert herb grower, Mel Thomas. He’s the author of Cannabis Cultivation: A Complete Grower’s Guide, 3rd Edition. It’s published by Green Candy Press. Mel’s a world-renowned cannabis cultivator and at one time was the largest producer of marijuana in the UK. Have a question for him? Then email us at stuffstonerslike[at]yahoo.com
QUESTION: What’s the Best Temperature for Growing Marijuana Indoors during both the vegetative state and flowering? I know some strains can prosper under different conditions. But, I just need a general idea. Also, what’s the best way to control temperature? Do regular household fans blowing under the lights help? I have two 600’s and I see temperatures in the low 90s pretty consistently.
MEL THOMAS: What’s the Best Temperature for Growing Marijuana Indoors, you ask? The recommended daytime temperatures for cannabis plants are:
Without supplemental CO2 21 – 26.5ºC or 69.8-79.7ºF
With supplemental CO2 rise to 26.5 – 32ºC or 79.7-89.6ºF
In the last two weeks of flowering 21 – 26.5ºC or 69.8-79.7ºF with CO2 reduced
Night temperatures should be kept above 15ºC or 59ºF
Measure your grow area temperatures using a maximum and minimum thermometer that will record the extremes of temperature reached. These thermometers are readily available at garden stores. Due to the heat given off by HID lighting systems, it is unlikely that you should ever need to heat a grow room during the daylight cycle. However, a thermostatically controlled air-blowing fan heater will maintain the night time temperature at the correct level and prevent any stress to the plants. Regular fans are great for air circulation but you will need some form of extractor fan to remove any excess heat and bring fresh air into the grow area.