Under glass, rain never reaches your plants. Everything they get comes from you, and in a hot spell that can mean watering tomatoes every day. Get the watering right and the rest of greenhouse growing gets much easier.
The basics
- Water at the roots, not over the leaves. Wet leaves in a warm greenhouse invite grey mould and mildew.
- Water in the morning. Plants have water for the hot part of the day and go into the night dry.
- Water steadily. Tomatoes that swing between dry and soaked get blossom end rot and split fruit.
- Check the compost, not the calendar. Push a finger in. If it is dry 2 cm down, water.
Drip irrigation
A drip kit runs a thin pipe past every pot or growbag, with a dripper at each plant. Connected to a tap with a timer, it waters on its own. It suits growbags and big pots on the floor. Check the drippers now and then, as they can clog.
Tap timers
A timer on the outdoor tap turns the water on and off at set times. Combine it with a drip kit and the greenhouse looks after itself while you are away for a few days.
Capillary matting
A thick felt mat on the staging, kept wet from a tray. Pots stand on it and draw up water from below. It works well for seedlings and small pots and needs no power or tap.
No tap nearby?
On an allotment or at the bottom of the garden, a water butt next to the greenhouse collects rain from its own roof.
How much water?
There is no fixed amount. A large tomato plant in a growbag in July drinks far more than a pot of basil in April. Watch the plants and the compost, and give more in hot, sunny spells.
Tips
- Put the drippers in before the plants get big and the greenhouse gets crowded.
- Stand growbags on the floor rather than on staging, as they dry out more slowly there.
- Shade netting in high summer cuts how much the plants need.
Our picks for drip kits, timers and matting are below.
