How to ventilate your greenhouse

A greenhouse is supposed to get warm and humid inside – only not too moist as it can damage the plants and cause various diseases. It would be best if you kept an eye on the humidity level in the greenhouse – no matter which kinds of plants you grow in there.  

Depending on the plants you have in your greenhouse, the temperature should be between 15 and 25° C – with a humidity level between 60 and 80 per cent. The plants will stop growing when the temperature drops to below 10 ° C - if the temperature drops to below 0 ° C; most plants will die or get damaged. On the other end of the scale, the plants will stop growing at app. 28-30 ° C as the photosynthesis stops. Most plants can only tolerate temperatures up to app. 40 ° C for a short time.

If the temperature, in general, is too hot in your greenhouse, the plants will lose a lot of water as they ‘sweat’ or ‘breathe’ water. Even if you water the plants regularly, the high temperatures will harm the plants and weaken them in the long run. The natural temperature change between day and night is also essential for the plants. In short, you must regulate the heat and humidity inside the greenhouse to get the right growth conditions. 

A hygrometer measures the level of relative air humidity and can help you control the level of moisture. An easy solution to control the humidity is our automatic window openers. Some of our many different greenhouses already have ventilation windows with automatic window openers installed when you receive them from us. Other models may only have manually operated ventilation windows, and here you have to open and close the windows whenever there is a need to ventilate the greenhouse. It is much easier with automatic openers, but the traditional windows have worked fine for many years. However, for some of the manual operated ventilation windows, you can order automatic openers and mount them on the windows.

A greenhouse may be a closed entity, but the temperature and humidity inside are still depending on many factors such as:

1. The weather outside
2. How well insulated the greenhouse is
3. The materials the greenhouse is made of – greenhouse film, glass, polycarbonate panes etc.
4. The floor inside the greenhouse – is it soil, cast foundation, frost-free etc
5. Numbers of ventilation windows or automatic ventilation
6. Heating systems

When we talk about the air humidity in a greenhouse, it means water vapour content in the air. The following applies: the warmer the air in the greenhouse, the more water vapour it can absorb. When ventilating in winter, the cold air from outside will get into the greenhouse and make the humidity drop. If you allow the cool air to go lower than the dew point, the water vapour will condensate – turn into water again. The condensation water first deposit on the cold surfaces of the greenhouse – walls and ceiling. This makes optimal growth conditions for unwanted mould.

Automatic ventilation technology for greenhouses

Automatic window opener

An automatic window opener does not require electricity as they run on a hydraulic system with wax or gas expands as the temperature increases or decreases. The expanding wax or gas moves a piston rod, which sets window levers in motion so that the ventilation window opens and closes. The windows often have a spring to secure closing the window shut when the temperature decreases and the window is closed. The automatic window openers ensure ventilation even when you are not present all the time. We recommend that you follow the indoor climate closely to make the plants' best possible growing conditions.

Electric fans
Electric fans can either get power from an ordinary electric socket or a solar-powered entity outside the greenhouse. We recommend installing a solar-powered fan with a battery to make sure that the fan works even when the sun is not shining – during cloudy days and the night. As opposed to ventilation windows that let out warm air slowly, the electric fan can remove warm air more quickly depending on the fan's size, so pay attention to temperature and more. As the automatic window openers, you can have electric fans which will start at a certain level of humidity, as you know from bathrooms and similar. The fans can be installed in a windowpane on the roof or a wall.