If your grow room feels warm or cold, humid or dry, that is a sign that you may want to look into changing the temperature or humidity of your grow area.
During late flowering, improvements to overall quality can be achieved by keeping temps and humidity as low as possible. Humidity under 40% RH is ideal.
The Vegetative Stage: Best Grow Room Temperature
Room temperature with lights on should be 18–24°C. Increase the difference between day/night temps by up to 10°C for even better results.
Cannabis plants like a temperature similar to humans, or a little warmer — not too dry, not too humid.
Basic Hygrometers and Thermometers
For a lot of indoor growers, that is all you need to worry about. If it feels too hot or too cold for you in your grow area, it’s probably too hot or too cold for your cannabis plants as well.
The best grow room temperature during the vegetative stage of growth is 70–78 degrees F. when the lights are on during the “daytime” and no more than 10–15 degrees cooler at “night” with a relative humidity of 45–55%. With these settings, your plants will best be able to convert light into energy for growth. This is the time when the plant puts on leaves and branches and expands it’s root system throughout your growing medium. If it gets too cold or hot, growth stops and you eventually risk losing your plants altogether.
The best grow room temperature during the flowering stage of growth is 68–75 degrees during the day and no more than 10–15 degrees cooler at night. If you’re supplementing with CO2, daytime temps can be as high as 75–82 or so. During flowering, you should lower your relative humidity to 35–45% and even lower (30%) for the last couple of weeks before harvest. This will help you avoid issues with mold, bud rot and PM (Powdery Mildew) that can arise in higher humidity.
Cannabis plants like a temperature similar to humans, or a little warmer — not too dry, not too humid. For a lot of indoor growers, that is all you need to worry about. If it feels too hot or too…
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Step 2: Refer to Temperature Chart
Too Cold: What To Do
Optimal Temperature At Different Life Stages
Too-cold air can cause buds to grow airy and loose
It’s good to aim for a temperature of 70-85°F (20-30°C), during the vegetative stage. It’s not always possible, but try to give plants slightly cooler temps during the dark period than during the light period as long as you stay within the recommended range.
Air Circulation: If there is a lack of proper air circulation in the grow room, you will tend to get hot spots that can damage your plants. It’s always a great idea to install fans in the grow room to help circulate the air inside the tent. Remember, don’t point fans directly at plants. Leaves can be rustling slightly, but stems should not be waving around due to the direct breeze of the fan. I like to point fans somewhat over or under the canopy, so it doesn’t aim directly at plants. Sometimes I point the fan at a wall to move the air around without blowing on the plants.
Consider Getting Different or Smaller Grow Lights: Learn about different grow setups.
Air Conditioner – (some are portable, some ACs fit in your window) – in addition to cooling the air, an AC will also tend to lower the relative humidity of the air. To be effective, and AC must be able to exhaust hot air outside the house, just like hot grow lights. If the air outside the grow tent is already too warm, you will need to get an AC to pre-cool the air before it enters the grow tent. No matter how strong your exhaust system, it won’t be able to bring the temperature lower than your ambient room temperature. If you need to lower the ambient room temperature, you’re going to need a way to cool the air, and air conditioners are hands-down the most effective way to cool your air.
Learn exactly how to maintain the rigth temperature for your indoor cannabis grow room.