What should the humidity be in a greenhouse?
The humidity for greenhouse production should be kept between the two extremes (with a relative humidity ranging from 70% to 94% at 25°C/77°F) as plants may start to suffer when the humidity is either too low or too high.
Low humidity level in the greenhouse
Low humidity in the greenhouse means a relative humidity (RH) of 70% or lower. The dry air causes the plants to transpire a lot and is sensed by plants as stress. To reduce water transpiration, plants will start to close their stomata (opening in leaves). Because of the closure, gas exchange is reduced and there is less inflow of CO₂ and outflow of O₂. This increased stomatal for CO₂ has a direct negative effect on the leaf photosynthesis rate. Low humidity also leads to smaller leaves because the cell elongation is reduced.
High humidity level in the greenhouse
More often, greenhouse crops suffer more from too high humidity than from too low humidity. A humid greenhouse should be dealt with as soon as possible.
Fortunately, greenhouse control systems can measure and control humidity in greenhouses effectively. A relative humidity above 94% reduces the transpiration rate of plants and increases stress sensed by plants.
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