How to Use Soil Heating Cables

Providing a source of heat at the base of seed trays, containers and pots will help encourage seeds to germinate and seedlings to grow strongly, giving them an essential head-start in life.  

Soil heating cables are an ideal way to provide this heat; they are flexible and very easy to use. In fact, constructing your own propagation area in the greenhouse is one of the easiest, yet most rewarding projects you can tackle. Here’s how to do it...

Firstly, you’ll need a suitable section of greenhouse staging or benching. A tray is best as you’ll need to cover the cables with sand, but try to avoid painted surfaces (the heat can discolour them) and check the tray surface is free of sharp objects – piercing the cable means it cannot be used.  

Next, select the length of cable for the size of area you want to heat the lay the cable in loops, roughly 8-9cm apart. Cover the looped cable with sand to a depth of 1-2cm then place your seed trays or pots on the heated sand bed.

Although the cables will raise the ambient soil temperature in the trays by 8-12 degrees C, you can influence the heat generated by the cable by placing material beneath. For example, to create a cooler propagation bed, position a paving slab or similar underneath the cables; and use polystyrene for a warmer bed.

Finally, you can gain even greater control over the performance of the cables by installing a thermostat. Each cable is supplied with a standard UK 3-pin plug, allowing the cables to be plugged into the mains,   and if the screw is removed from the centre of the plug casing the top will flip up to reveal a European 2-pin version; ideal for plugging into a thermostat!