Humidity for plants – Metrop. Humidity in a cultivation room is perhaps the most underrated growth factor. We use relative humidity RL as a unit to measure this and to make adjustments. A dry air will accelerate the evaporation of the moisture from the leaf and a very moist air will delay this. A plant must always evaporate some water so that there is room in the plant for new water from the medium in which new nutrients are dissolved.
The plant is like a pump that works on solar energy. However, if the relative humidity around the plant is too low, the plant will evaporate more than it can absorb and the plant will experience a growth disorder and may eventually dry out. If the humidity around the plant is extremely high, the plant will eventually grow little. A balance in this is therefore very important. Small cuttings still have very little root and therefore cannot absorb much water. If the humidity is to low around the cutting, the cutting will vaporise quick it inside water without able to absorb new water.