More often people are seeking to reduce humidity. However, humidity addition can be needed in some very dry climates, or for particular humidity-loving crops. Humidity itself is not always bad inside the greenhouse, in fact, it is important for keeping plants cool. When there is excess humidity that forms droplets on greenhouse plastics, that can be problematic and encourage pests and pathogens.

Foggers and misters are the most common types of equipment used to keep the environment in the greenhouse humid. Humidity helps plants cool themselves, like sweating for humans, and can be very important when cloning plants. Humidity is relevant to temperature, so humidity recommendations generally assume the temperature will be around 25°C. Even slight increases in temperature such as 28°C can increase the potential for pests and pathogens.

Foggers create water particles less than 50 microns (0.002”) in diameter. High-pressure greenhouse fog systems can create droplets as fine as ~10 microns in diameter. Misters create water particles range from 50 to 100 microns in diameter. The tiny droplets of water created by foggers and misters evaporate into water vapor quicker the smaller they are. Larger droplets produced by misting tend to form condensate more readily on the plant surface or saturate growth medium. Fogger systems are ideal for increasing humidity for propagation, but mist systems can be just as effective so long as the user is aware to look out for excess moisture accumulation.

Instead of using a fogger or mister, it is a better long term option to invest in a greenhouse humidifier. These will produce a more stable and reliable greenhouse climate that can be controlled with more precision. Humidity can be monitored using indicator cards, but more accurate monitoring will be accomplished by using a temperature and humidity data logger, or most accurately with an environmental sensor with app alerts. Monitoring humidity is important because you do not want excessive amounts of humidity to build up. Pests and pathogens thrive and spread in condensation so it is very important to prevent condensation from forming. The best way to do that is to keep temperatures and humidity consistent. HAF fans for circulatory airflow help mix the air inside the greenhouse to keep conditions stable. They are a great addition to any greenhouse using automated heating, cooling, and/or humidification/dehumidification.