Humidity, to a certain extent, determines how much water your plants will consume. The dryer the air, the more they will consume. When they are young, cannabis plants prefer higher humidity levels that tend to promote faster growth. Their leaves will pull water directly from the air to grow foliage while the plant develops its root system. As the plant matures, however, a lower humidity level should be established to prevent formation of mildew or mold.
Relative humidity (RH) is a measure of the amount of moisture in the air compared to what the air can sustain at a given temperature. Cannabis growers typically develop strategies to manage relative humidity at each stage of growth (see graph on right).
Temperature and relative humidity are closely interrelated. If the temperature is too hot and dry there is potential for the air to extract moisture out of the plant resulting in slower growth. Cool and humid conditions, on the other hand, can cause mold or fungus as well as slow growth. Controlling both temperature and RH at the same time is imperative to achieving optimum growing results. Read more below.