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.
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.
Prevent soil from contaminating the aggregate by lining the trough,
trench or floor with thick polythene with drainage holes every meter.
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 bituminous 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 neighboring 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 fertilizer 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.