Humidity has a direct impact on plant growth. Due to the nature of greenhouse and hydroponic setups, controlling the humidity in this environment can be difficult. Humidity levels change with fluctuations in temperature and plants are constantly transpiring, adding to the problem. The temperature is quite different both at day, night, summer and winter, which makes the humidity hard control. If left untreated the high humidity environment will cause many problems for plant growth, such as reduction of water uptake due to foliar and slow drying of growth medium after watering resulting in root diseases. When your RH breaks 85 percent you may get fungal issues due to transpired moisture remaining on the leafs. These compound to result in a lower quality crop and poor yields.
Humidity and Vapor-Pressure Deficit
Relative humidity is a measure of how much moisture is in the air relative to how much it can hold. Water holding capacity of the air doubles roughly every 11°C. This means air at 31°C can hold double moisture compared with that at 20°C. Therefor relative humidity isn’t a good measure to go by for deciding humidity levels in a greenhouse.
Vapor-Pressure Deficit is the difference between how much moisture is in the air and how much moisture the air could hold at full capacity. Plant leaves open their stomata based on humidity and vapor-pressure deficit, therefore controlling vapor-pressure deficit is a better way to improve plant growth. The below chart is a good rule of thumb for choosing your target relative humidity to achieve a good vapor-pressure deficit.
Choosing the Right Dehumidifier for your Greenhouse
When choosing a dehumidifier for a green house you need to keep in mind air circulation and uniformity. If you put a single dehumidifier in a greenhouse with no ducting, the area around the dehumidifier will be dry. However the areas further away won’t be dried effectively. Our solution to this problem is to use ducted dehumidifiers. With this method you can have large dehumidifiers and run ducting over a larger area. This reduces the need for fans and helps create a uniform humidity level in your greenhouse.