The right temperature for an optimum crop


Beginner's Guide: the right temperature for an optimum cannabis crop

Cannabis likes a comfortable room temperature when growing indoors, or a little warmer - not too dry, not too humid. For a lot of indoor growers, that's all you need to worry about. If you feel too hot or too cold for you in your grow zone, it is probably too hot or too cold for your cannabis plants.

Ideal temperature

The best temperature to grow cannabis is usually between 68-77 degrees (20-25 Celsius). If the ambient temperature around the plant drops well below 20-25 degrees, the plant's growth will slow down and its potential yield will be inhibited or even stopped altogether. As a result, the plant never matures… It is important to note that temperature is very important during a “day” cycle, when you let your plant get light. This is when photosynthesis and growth potential kicks in. In addition, there should be no big change in temperature between day and night.

If your plant's temperature goes above 77 degrees (25 Celsius), the plant's metabolism will speed up. So it will then ask for additional elements: more light, more water, more carbon dioxide, and more fertilizer etc ... Make sure to adjust the changes according to the temperature.

In other words, the ideal temperature

It is wise to invest not only in a thermometer, but in a thermometer attached to a ventilation or heating system, so that automatically manages the temperature in your growing room. An automatic system can also produce excellent ventilation for fresh air and to avoid carbon dioxide deficiency.

Vegetative and flowering temperature

Vegetative stage: Young growth cannabis plants in the vegetative stage prefer warmer weather than the flowering stage, in the range of 70 to 85 ° F (20-30 ° C). Learn more about the times in the vegetative phase.

Flowering phase: at the flowering stage (when the cannabis plants start to bud) it is best to keep the weather slightly cooler, around 65 to 80 ° F (18-26 ° C) to produce the best color, trichome production and smell. There should be a 10 degree difference between the night and day times for the best results. This is especially important in the flowering stage for the development of the highest quality buds.

Temperature too low

When the temperature approaches freezing, it is too cold for a cannabis plant to survive without damage. Colder weather will tend to slow growth. Temperatures below 60 ° F (15 ° C) tend to disrupt plant growth and freezing temperatures shock or even kill a cannabis plant.

Frozen weed ...

Plants are more sensitive to certain types of mold when they are fresh, especially if they are also wet. Warmer weather and large fluctuations in temperature contribute to excessive leaf size and can also reduce photosynthesis.

A plant that is grown in relatively cold weather can survive, but it will never grow as quickly or as well as a plant that receives the proper temperatures. Indoor plants tend to be much more sensitive to the cold than plants grown outdoors.

Temperature too high

While cannabis plants don't usually die of heat, temperatures that are too hot will cause plants to grow much more slowly. Note that temperatures above 26 ° C (80 ° F) in the flowering stage will not only slow bud growth, but may reduce the potency and odor of your buds. Controlling the room temperature is especially important in the flowering stage!

Too hot ...

In heat, cannabis is also more susceptible to many problems, including mites, powdery mildew (especially if it is wet too), root rot, nutrient burning (from increased sweating of water), increased stretch, wilt caused by oxygen from the root Deprivation and reduced "odor" of the buds (as terpenes can burn at higher temperatures).


The ideal moisture in the cannabis plant environment is between 40-70%. To measure the humidity you need a hygrometer. An electric hygrometer is probably the best choice for most growers. It often has automatic features that offer more control than just moisture. Which is always good for indoor culture.

Ambient humidity is an important factor (which also regulates temperature)

If the moisture of your plant goes below -40%, the plant will have a accelerated perspiration rate. There will be no big consequences. Your plant will simply consume water faster. As long as there is plenty of water in reserve, there is no problem. On the other hand, if the humidity is too high, your plant may have champignons, especially during the flowering period. And there, things rot very quickly ... You will certainly need to dehumidify manually, in order to solve the mold problems and the consequences that result from it.

Where to measure?

The temperature must be measured at the level of the canopy and in the shade of the leaves. The canopy represents the tops of the plants, as close as possible to the lamp. The highest temperature is evaluated.

The temperature peak is (indoor) near the canopy

When measuring in the shade, it represents the heat of the ambient air. As we would with the weather. Here we measure the heat of the air. This measurement is made from the stomata. A stomata is a small orifice present in the epidermis of aerial organs of plants (on the underside of leaves most often). It allows gas exchange between the plant and the ambient air (oxygen, carbon dioxide, water vapor, etc.) as well as the regulation of osmotic pressure.

Focus on cannabis stomata

So we measure on the stomata of the horizontal leaves, while remaining on the upper epidermis which is directly illuminated. We note that it is from 28 / 29 ° C as the stomata begin to close. Therefore, the temperature must be below this fateful limit. And therefore on the temperature measurement where the stomata are located. That is to say in the shade of the leaves.

Tags : Agriculture / GrowNewsPlanting

The author Weed-master

Weed media broadcaster and communications manager specializing in legal cannabis. Do you know what they say? knowledge is power. Understand the science behind cannabis medicine, while staying up to date with the latest health related research, treatments and products. Stay up to date with the latest news and ideas on legalization, laws, political movements. Discover tips, tricks and how-to guides from the most seasoned growers on the planet as well as the latest research and findings from the scientific community on the medical qualities of cannabis.