Greenhouse crops, especially tomatoes, are liable to many soil-borne pests and diseases. Ring culture, where bottomless pots rest on a bed of porous aggregate (such as gravel), prevents root diseases and also allows roots access to a large volume of consistently moist material.
Tomatoes are ideal for ring culture as they are very susceptible to soil-borne problems and having strong roots means they can take advantage of the large volume of aggregate. Other crops are less likely to benefit but aubergines, chilli peppers, chrysanthemums and sweet peppers could be grown in this way.
When to start
Prepare the aggregate bed a couple of weeks before planting young tomatoes and other crops into their positions in April.
Try using gravel, hydroleca or perlite as your aggregate.
Setting up a ring culture system
- Thoroughly clean the growing area to avoid the aggregate becoming contaminated with debris from preceding crops or infected soil.
- Make a trough or dig a trench to contain the bed of aggregate. The minimum depth is 15cm (6in), but no more than 25cm (10in) is usually used. Covering the entire greenhouse floor with aggregate is also possible.
- Prevent soil from contaminating the aggregate by lining the trough, trench or floor with thick polythene with drainage holes every metre. The aggregate bed needs draining, as standing water will harm plants. Waterproof troughs are possible but need careful managing to avoid root problems.
- The bed should be made far enough in advance of setting out the plants for it to warm up – two weeks should be sufficient.
- Fill bottomless containers, (25cm (10in) diameter, 30cm (12in) tall) with growing media (that used in growbags is ideal) and plant young plants in April. Special pots of bituminized paper are available for this purpose, but you can use any container that is open at the base.
- Leave the newly potted plants on the greenhouse floor, not the aggregate. As the plants grow, space them out so that the leaves of neighbouring plants never touch. This will avoid leggy growth.
- Once established, when the roots are showing at the bottom of the pot, place the pots on the aggregate with a close, firm contact between compost and aggregate. Spacing is the normal distance for indoor crops.
- Keep the aggregate moist and water the pots two or three times a week adding liquid fertiliser if growth is pale or insufficient. The tomatoes are then grown in the usual way.
After the crop is finished, remove the aerial parts of the plant and ease the roots out of the aggregate and discard.
Clean and disinfect the aggregate after clearing the crop. The material can be used for many years unless problems arise. To avoid polluting watercourses and ground water, aggregate should not be cleansed in situ, but lifted, washed and the disinfectant solution safely disposed of, according to the manufacturers' instructions.