This is when there is too much moisture in the air to remain in the vapor state. Condensation on plants occurs when leaf surface temperature is below dew point. This relationship is important in managing humidity in the greenhouse.ĭewpoint temperature indicates the temperature at which water will begin to condense out of moist air. In the range of temperatures encountered in a greenhouse, for every 20° F rise in dry bulb temperature, the water-holding capacity of the air doubles, and the relative humidity is reduced by one-half. Air at 70° F will hold twice as much moisture as air at 50☏. Warm air has a higher moisture-holding capacity than cooler air therefore as the temperature of air increases, the relative humidity decreases even though the amount of water remains constant. This term can sometimes be misleading, because it is temperature-dependent. The amount of moisture in the air is generally expressed as relative humidity (RH), which is the ratio between the weight of moisture actually present in the air and the total moisture-holding capacity of a unit volume of air at a specific temperature and pressure. Relationship Between Temperature and Humidity

This is accomplished through cultural practices and environmental control strategies. The key to successfully suppressing diseases is to keep the plant canopy dry, especially from dusk to dawn. Dripping water from condensation on the greenhouse covering also wets plant surfaces and spreads plant pathogens from plant to plant by splashing soil and plant debris. This moisture promotes the germination of fungal pathogen spores such as Botrytis and powdery mildew. At night as the air cools to the dew point, condensation occurs and water droplets are formed on cooler surfaces such as the leaves and glazing. The warm air holds the moisture in the vapor form. Sunny days increase the transpiration of moisture from leaf surfaces and evaporation from soil. The fall and spring are times when humidity related diseases usually peak in greenhouses.

Trap crack open a cold one