A soil warming cable is the ideal way to propagate seeds and cuttings on a greenhouse bench or in a cold frame.  The soil in the greenhouse takes time to warm up naturally; with a soil warming cable you are able to plant earlier and raise better specimens.

A simple frame can be constructed from wood to form the propagating area required, which is then lined with polythene.  The cable is laid onto 5cm of sharp sand (horticultural) and covered with a further 5cm of sand.

Cable is laid in runs 7.5 - 10cm apart.  This layout will allow you to raise the soil temperature by 11 - 13°c, assuming a greenhouse temperature of 7°c.  Higher temperatures can be achieved by laying the cable runs as close together as 5cm.  In this case the thermostat should be used to precisely control the soil temperature-meeting the differing germination requirements of various varieties of seeds.