Culture & Grow

The right temperature for an optimum crop

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

Cannabis loves a comfortable room temperature by growing indoors, or a little warmer - not too dry, not too humid. For many interior producers, that's all you need to worry about. If you feel too hot or too cold for you in your growing 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 falls well below 20-25 degree, plant growth will slow down and its potential yield will be inhibited or even halted altogether. As a result, the plant never matures ... It is important to note that the temperature is very important during a "day" cycle, when you let your plant take the light. That's when photosynthesis and growth potential come into play. In addition, you do not need a big temperature change between day and night.

If the temperature of your plant goes beyond 77 degrees (25 Celsius), the metabolism of the plant will accelerate. So it will then ask for additional elements: more light, more water, more carbon dioxide, and more fertilizer etc ... Make sure to tune 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 cannabis plants start to bud), it is best to keep the weather slightly cooler, about 65 to 80 ° F (18-26 ° C) to produce the best color, trichome production and smell. There should be a difference of 10 degrees between the night and day times for the best results. This is especially important in the flowering stage for the highest quality bud development.

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.

From the 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 appropriate temperatures. Houseplants tend to be much more sensitive to cold weather than outdoor plants.

Temperature too high

While cannabis plants do not usually die of heat, too hot temperatures 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 bloom stage!

Too hot ...

In the heat, cannabis is also more prone to many problems, including dust mites, white powdery mildew (especially if it is wet too), root rot, nutrient burning (from increased sweating). water), increased stretching, wilting caused by oxygen from the root Deprivation and reduced "smell" of 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 the 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, to solve the problems of mold and the consequences that result.

Where to measure?

The temperature is measured imperatively at the canopy and in the shade of the leaves. The canopy represents the top of the plants, closer to the lamp. The highest temperature is evaluated.

The temperature peak is (indoor) near the canopy

When measured 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 done from the stomata. A stoma 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 ...) as well as the regulation of the osmotic pressure.

Focus on cannabis stomata

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

Tags : Agriculture / GrowNewsPlanting