Soil warming cable
Line a wooden frame with polythene. The cable is laid onto a 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 11-13deg.C, assuming a greenhouse temperature of 7deg.C. Higher temperatures can be achieved by laying the cable runs as close together as 5cm. In this case a thermostat should be used to precisely control the soil temperature meeting the differing germination requirements of various varieties of seeds.
0.45m (4'sq) - 3.05m (10ft) 50 watt
1.75m (16'sq) - 12.2m (40ft) 150 watt
3.85m (36'sq) - 24.4m (80ft) 300 watt
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