Watering Greenhouse Crops

Check the roots before deciding to water. The same greenhouse can contain a dry seed tray, a moist bed and a large tomato needing more water than either. One fixed daily dose will not suit them all.

By Simon Adams · Updated 25 October 2026

Check moisture below the surface

Feel the compost below its dry-looking top layer and compare pots by weight where practical. Check each container rather than assuming neighbouring plants are equally wet. Water slowly when needed, aiming to moisten the root zone and stopping as drainage begins. Keep drainage holes clear and avoid leaving ordinary pots standing in water.

Containers depend on a limited supply of compost and can dry much faster than beds. A newly planted crop also has a smaller root system than an established one. Put small pots and young plants on your checking route first.

Water beds at the roots

Rain outside does not refill a covered greenhouse bed. Check soil moisture where roots are growing, not only beside the doorway. Apply water to the soil so it reaches the crop rather than wetting paths and foliage. Seedbeds and seedlings need particular attention while establishing.

A useful routine is to divide the greenhouse into watering areas: seed trays, small pots, large fruiting plants and beds. Check each group, then decide what actually needs water. The routine should prompt an inspection, not an automatic soaking.

Keep fruiting crops evenly supplied

For tomatoes, aim for even soil moisture. Repeated drying followed by heavy watering can contribute to fruit splitting and blossom-end rot. Large container plants may need daily checks or more in hot weather, but the amount should follow the compost, plant size and conditions.

If a plant wilts, inspect moisture before adding more. A wet rootball and a dry one require different responses. Also look at heat, root health and drainage; do not keep pouring water into already wet compost.

Check an irrigation system where it matters

Drip irrigation can make watering more manageable, but a running timer does not prove that every crop receives enough. Check the soil beside several outlets, including the end of the line. Look for blocked drippers, leaks and differences between pots. Review settings as crops grow and the weather changes.

Before going away, test the whole arrangement under working conditions and leave clear instructions for any backup helper. Keep the arrangement simple enough that a fault is easy to spot.

Adjust through the season

Morning watering gives you time to notice dry plants and deal with problems. In colder, dull weather, plants commonly use less water; keep checking but reduce unnecessary watering. More summer heat calls for attention to ventilation and shade as well as root moisture.

Record useful observations, such as which pots dry first and how long a watering run takes to reach the root zone. Build your routine around those checks rather than copying a litres-per-plant rule from a different greenhouse.