When plants grow, they absorb water through their roots and release it as water vapour through their pores. They sweat, just like we do. The extent to which this happens depends greatly on the moisture content of the air in the greenhouse. The drier it is, the faster the plants will appear. The risk is that they will then wither away because they lose too much water. To prevent such problems, you should therefore keep the humidity in your greenhouse to a minimum. The humidity is directly related to the temperature in your greenhouse. The higher the temperature, the more humid the air can be. The amount of water in the air is expressed as a percentage that corresponds to the amount of water vapour in the air compared to the saturation at a certain temperature. This measurement is made with a hygrometer that reads like a thermometer. Nowadays there are electronic devices that show this percentage directly on their display.
The air is said to be humid when the hygrometry at 20°C reaches and exceeds 75%. If it falls below 35%, the air is dry. Most plants grown in greenhouses need a humidity of between 40 and 75% during their growth phase. Tropical plants appreciate humidity close to saturation because they draw water from the air through aerial roots. However, be careful if the humidity in your greenhouse exceeds 80%. The conditions thus created are then favourable to the rapid development of grey mould and noodles!
In winter, it is best to keep the humidity at a low level (25 to 40%). Good humidity in the greenhouse also prevents accidents due to premature overheating during periods of strong sunshine. It moderates excessive temperature fluctuations. The easiest way to increase and maintain the humidity in your greenhouse is to spread water over the ground with a watering can or hose. You can also store water in some shelves. If your greenhouse is small, reserve a small sprayer for this task. However, you will need to spray once or twice a day for this, or even more in very bright sunshine. A terracotta humidifier can do this.
Collect rainwater
Take advantage of the roof surface of your greenhouse to collect rainwater. It is free and available. To do this, install gutters at the foot of each slope and place a collection tank at the outlet of each downpipe. Equip each tank with a lid to prevent a child from falling in and to prevent the water from turning green under the influence of light. The water is collected by dipping a watering can into it. Better yet, if you have taken the precaution of mounting the watering can on a fairly high support, fill your watering can using a tap installed at the base.