Humidity in a grow room is perhaps the most underestimated growth factor. To measure and adjust it, we use relative humidity (RH) as the unit.
Dry air speeds up evaporation of moisture from the leaf, while very humid air slows it down. A plant must always evaporate some water so that there is space inside the plant for new water from the medium, in which new nutrients are dissolved.
The plant works like a pump powered by solar energy. However, if the relative humidity around the plant is too low, the plant evaporates more than it can absorb, which causes growth disorders and can eventually dry the plant out.
If the humidity around the plant is extremely high, growth will eventually slow down drastically. Balance is therefore very important.
Small cuttings still have very few roots and therefore cannot absorb much water. For strong cuttings, a humidity of 80% in the cutting room is required.
If the humidity around the cutting is too low, it evaporates water quickly without being able to take in new water.
In the first 3 weeks of growth, plants need a humidity of about 70%–80%.
After that, until around week 6, the optimal humidity for plants is 60%. From week 7 onwards, humidity should be lowered again, but not below 40%.
Below 40%, evaporation happens very quickly, making it very difficult for the plant to replenish moisture in time. The plant closes its stomata, which stops growth and flowering. Downtime always comes at the expense of yield.
Humidity temperature is also important.
Some systems can easily blow cold water into the air. However, this cold moisture will naturally slow down growth. It is best to use lukewarm water.
Hobby growers who do not have a humidifier can best spray the leaves regularly during the first 4 weeks.