Looped 4"-6" below the soil surface, this cable works like an underground sun to heat the soil and speed germination and seedling growth with gentle bottom heat.Works best in an enclosed, insulated, and covered planting box. Not designed to work in outdoor beds. A built-in thermostat automatically activates the cable when soil temperature drops below 74°F. (But please note: This does not mean that soil temperature will reach 74°F.) The cable plugs directly into 110V outlets and uses 42 watts/12 ft. It is designed to prevent shock danger in wet conditions. Use approximately 4 linear feet of cable per sq ft. Protect the cable by laying a wire mesh screen over it before covering it with soil. (If you want to test the cable, put it in the fridge for an hour, take it out of the fridge, then plug it in. The cable should warm up.) Caution: Never allow the cable to cross or touch itself while plugged in or the heating cable will not function properly.