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There are many environmental factors that affect plant growth, and in this article, we want to talk about the impact of indoor humidity on cannabis cultivation.

The humidity is formed by the evaporation of soil moisture, the water replenishment by spraying, and the transpiration of water in plants under the condition of airtight facilities.

Many novices will overlook the indoor humidity when they grow marijuana. But humidity can always affect the quality of cannabis plants. The humidity affects the transpiration of cannabis plants, and transpiration is not only the driving force for water absorption but also the driving force for mineral nutrient transport. When the humidity is high, the transpiration effect is small, and the ability of plants to transport nutrients decreases. Transpiration can also adjust the temperature of the leaves. If the temperature is high, the humidity is high, and the transpiration is small, the leaves may be burned. If the air humidity is too low, the necrosis of the leaf edge and the leaf tip will be caused.The humidity affects the opening and closing of plants stomata. Too high or too low humidity will cause the stomata to close. Plant stomata are close, carbon dioxide cannot enter mesophyll cells, and photosynthesis will slow down or even stop.

What will happen if humidity is too high or too low?

If it’s too humid, mold growth can destroy the entire crop.Bud rot and white powdery mildew usually appear in high humidity environments.

Bud rot is a mold that develops in the dense core of cannabis buds. Infection begins at the shoot and spreads further outward from there. It destroys the surrounding buds, turning white, grey, and finally black, and a sticky mush. At that point, the buds can no longer beused.

White powdery mildew is one of the easiest diseases to spot on the leaves, and its symptom appear on cannabis leaves as a white powder that looks like baking soda has been sprinkled on the leaves. Once these symptoms appear, marijuana becomes fully infected and largely irreversible. Powdery mildew can affect a plant’s ability to absorb nutrients, causing leaves to discolor and wilt.

If the environment becomes too dry (low humidity),your plants lose more water than they regain through the roots. If this happens, the growth will become stagnant. Your plants will close the pores on the leaves to minimize water loss. This is an effective strategy, but it means they absorb less carbon dioxide from environment. The result is cell death within the cannabis plant.
Or, if roots are a bit more developed, low RH will make the young plant drink excessively which will often lead to “nutrient burn,” characterized by brown tips on your leaves.

What is the optimal humidity?

Optimal humidity depends on the stage of the cannabis. From germination to late flowering,  the cannabis plants require different humidity levels. Since each stage comes with distinct metabolic reactions, the relative humidity needs also vary.

-Seedling stage: ideal level is 65%-70%
High humidity levels allow water intake through leaves, seedlings will stay healthier and root faster in warm, humid conditions

-Vegetative stage: ideal level is 40%-70%
During the plant growth phase, as the plant begins to take root, the roots absorb more water, which evaporates through the leaves to help cool the plant. As the plant transpiration, the air humidity also increases, so the humidity level can be reduced by 5% per week.

-Flowering stage: ideal level is 40%-50%.
The moisture is reduced to this level mainly to prevent the growth of mold which is very vicious at this stage.

-Late flowering: ideal level is 30%-40%
Gradually lessening the humidity in the final flowering stage is essential to maintain leaf and bud quality. This can ultimately help improve the yield, flavor, and appearance of the plant.

How to keep the optimal humidity?

You will need a hygrometer to monitor the humidity levels in the grow room.