Monitoring Humidity in Greenhouses

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An important aspect of agriculture and, more specifically, humidity in greenhouses. Since greenhouses are enclosed, they are subject to variations in humidity that aren’t present in open-air growing environments. Too much or too little humidity, like water, can cause issues for growers. Too little water/ humidity and your plants wither away; too much water/humidity and they may rot or get fungal infections.

During the spring and autumn, plants in a greenhouse can be affected by fungal diseases if humidity is not controlled. During this time humidity tends to be higher because of the warm sunny days and the cool nights. The water in the soil is more likely to evaporate and transpiration, the passage of water vapor through a membrane or pores, in leaf surfaces increases. This moisture is stored as vapor in the warm air. During the night the air then cools and condensation occurs. These conditions may cause Botrytis and other fungal diseases; these spores are spread as the condensation forms droplets and seep into the soil.

If the humidity is too low the plants may transpire at a rapid pace causing them to lose a large amount of moisture. Often a plant will wilt under these conditions if additional water is not available at the roots. The desired humidity level for good plant growth is, between 50-85%.To maintain this level of humidity, it is recommended that greenhouse growers use hygrometers to measure the humidity in the greenhouse.


A grower from a greenhouse was looking for a thermohygrometer. The main criteria were that it had to be a portable, accurate over a wide range, and be affordable. The HI9564 was recommended. It measures humidity from 20.0 to 95.5% and has an accuracy of +/- 3% from 50 – 85% RH and +/-5% outside the range. The customer appreciated the min/max buttons allowed readings to monitored for changes during the day. The customer also appreciated the auto-off feature that turns the meter off after 20 minutes to maximise the battery life. The HI 9564 has a 250-hour battery life using a single 9V battery and also has a calibration feature that allows for single point calibration to a set value.