Now you can start vegetable, flower, and herb seedlings just like the professional bedding plant growers do. Soil Heating Cables can be used indoors or outdoors in cold frames or greenhouses. Bury the cables in soil or soil-based mixtures so that no portion of the colored heating section is visible. The cables use 3.5 watts per linear foot. Use 4 linear feet of cable to warm each square foot of planting area. The built-in thermostat automatically activates the cable when the soil temperature drops below 74°F. Complete instructions included.