This method ofmakes use of the fact that water rises by capillary action in a suitable , so long as the base of the pot is in contact with a moist medium.
Plasticwhich have a ring of holes lend themselves well to this method, and some pot plant growers find they get very good results by using peat-based composts.
It is essential that the pots stand level and that the base of the pot rests firmly in the sand used on the benches, in fact pots are slightly screwed down into the sand, to begin with. (Capillary matting is also often used.)
Benches can be fitted with trickle irrigation tubing and the amount of water fed through the system can be controlled by a time clock. It is important that the sand on the benches should be kept moist at all times. Lay flat tubing is also used as is plastic piping drilled with holes at 300mm intervals. The number of trickle lines will vary according to the width of bench but are usually 450mm, or so apart.
Irrigated benches should be level and the depth of sand used is 75-100mm. The sand is laid on a polythene sheeting but the sides must allow water to drain away freely.
If clay pots are used, it is necessary to insert a fibre glass wick into the drainage hole to ensure passage of water from the sand on the bench up through to the compost in the pot.