The key elements of greenhouse success are temperature and humidity. Temperature can be controlled with heaters, shades and insulation, while humidity is controlled through the introduction of water and air.
Shading and watering is particularly important in the warmer months. Shading protects plants from direct sunshine, which can scorch tender leaves or lead to wilt, and helps to keep the internal temperature down. As a result, any shading should be removed as soon as the temperatures start to drop to enable the greenhouse to benefit from the sun’s warmth.
In addition to providing plants with the essential water they need, why else do you need to keep the air damp? Many greenhouse crops will cope with the consistently higher temperatures of summer, or even spring and early autumn, if the air inside the greenhouse contains enough moisture and is ventilated well. Humidity in the air will also help to reduce the temperature inside your greenhouse.
Watering is most effective when it is done regularly; for most plants, little and often is better than a massive deluge once a week. Some plants, such as chillies, need more watering than others, so be aware of your plants’ differing needs. An irrigation system can help you to keep on top of watering and is readily available and fairly simple to install.
Try to avoid splashing the leaves during watering. Greenhouse plants are prone to mildew and botrytis-type diseases, which watering the soil rather than the leaves can help to prevent. Regular checks on your plants will help you to spot any signs of disease or infestations, such as spider mites, and you can take the appropriate measures to deal with them. Keeping your greenhouse tidy will also help to prevent diseases taking hold.
You can also use the damping down approach to boost humidity in the air. This involves wetting the hard surfaces, such as the floor and shelving, and allowing them to dry naturally. This creates a good level of relative humidity, which is beneficial to the plants. Damping down will also help to cool temperatures. By watering the ‘air’ rather than the plants, gardeners can again reduce the risk of infection.
The damping down is best done in the morning, although the process can be repeated several times during the day in especially hot weather. You can use a hose or watering can; again, take care to avoid splashing the plants.
Ventilation is simply controlled by opening and closing vents, whether manually or automatically. Keeping a good flow of air is really important to cool the greenhouse and keep your plants healthy and strong. If you are lucky enough to live in a warmer part of the UK, it is worth considering buying a fan.