What Is The Optimal Cannabis Temperature?

Growing marijuana indoors allows cultivators to control everything about the environment, ranging from how much light their plants get to the level of CO2 found in the air they breathe. One of the most important factors contributing to plant health and growth is temperature. Temperature affects everything from how quickly seeds germinate to how well the finished product cures, so it should be regulated carefully throughout the growing, drying, and curing processes.

The Effects of Temperature on Growth

Unlike most animals, cannabis plants don’t create their own body heat. They’re reliant on external sources of heat to stay warm. That doesn’t mean they don’t have any natural mechanisms for controlling temperature, though.

Plants use a combination of external heat and evapotranspiration to regulate internal temperatures. That means the temperature reading on a thermometer won’t perfectly reflect the temperature of the plants themselves.

Most growers realize that plants left in an uninsulated and unheated room will almost certainly die if they are exposed to below-freezing temperatures at night, but they don’t always know that plants also suffer from excessively high heat, especially in combination with high humidity. For now, growers just need to know that while marijuana plants can survive within a pretty large temperature range, they require a much narrower temperature range to thrive.

Finding the Optimal Temperature

Before anything else, growers should take factors such as the strain’s extraction rates, the number of lights, ventilation, and the size and location of the grow room into account. Once these have been addressed, it is time to determine the best temperature.

To put it simply, marijuana thrives best when exposed to a comfortable environment. However, comfortability is relative to its growth stage. Generally speaking, cannabis goes through three stages before reaching harvest:

Seedling. Because of their underdeveloped root systems, seedlings need loads of light and heat. But, because they are quite young, they cannot tolerate high temperatures. Therefore, it is recommended that growers maintain 20ºC to 25ºC environment when the light is turned on.

Humidity levels should also be high. As alluded to earlier, humidity and temperature go hand and hand in the development of a plant. A level between 65% and 70% is enough for seedlings to absorb water through their leaves.

Vegetative. As cannabis plants grow older, they become more robust. It starts to be more resistant to heat and cold. During this time, the temperature may be raised up to 30ºC.

As the roots can absorb a good amount of water, growers may lower the humidity levels by 5% for each week that passes. Ideally, the range should be around 40% to 70%.

Flowering. In the final phase, breeders can benefit from maintaining temperatures similar to when the plants were seedlings. By keeping the temperature at 20ºC to 26ºC, buds avoid having their terpenes burnt off. And, so, it can produce flavorful flowers that are potent.

Humidity levels should be kept low too, at a 40% to 50% limit. Lowering both the temperature and relative humidity levels as the plants move to the late flowering stage is also a smart move.

Growers should take note that suggested temperature difference for when the lights are turned off is 5ºC. This is applicable to all stages of development.

7 Essential Concepts About Temperature Control

1. Ventilation kit – Hot air should vent out of the grow space if heat is a problem. Vent air to the outdoors if you want to prevent the hot air from being recirculated around the grow room.
2. Fans only push air around – It’s a common misconception that fans bring down the temperature, but fans don’t cool the air. They provide a breeze and help level out the temperature within an area. If it’s hot in your grow tent but cool in your room, then a fan will help equalize the temperatures. But if your entire room is too hot overall, then fans won’t bring the temperature down.
3. ACs and Evaporative Coolers bring the temperature down – Besides exhausting your heat outdoors, the only way to bring the temperature down is to use an AC or Evaporative Cooler. Note: An AC will work in any climate, but evaporative coolers need dry air and only work when the humidity is under 30%.
4. Strain makes a difference – Heat and cold bother certain plants more than others. The strain has a significant effect on a plant’s heat or cold resistance. 
5. Choose the right light schedule – Too hot during the day or too cold at night? Switch your timer’s on/off cycle, so your cannabis grow light is on at night and off in the day. Switching the time your grow lights are turned on will help equalize day and night temperatures. It may even reduce your electricity bill as some people get charged less for electricity used at night. Keeping grow lights off during the day will help with heat, while your grow lights being on at night will keep plants warmer when it’s the coldest.

Conclusion

The ideal temperature for growing cannabis is somewhere around 25°C. But remember, this can vary slightly from one plant to another. Whenever you’re working with a new plant, feel free to play around with the temperature settings in your marijuana grow tent a bit, and see how they affect your plant. You’d be surprised just how much variety there is in the world of growing cannabis.

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