average ground temperature below frost line
Throughout most of the U.S., the temperature of the ground below the frost line (about 3 to 5 feet below the surface) remains at a nearly constant temperature, generally in the 45 Â° -50 Â° F range in northern latitudes, and in the 50 Â° -70 Â° F range in the south.hroughout most of the U.S., the temperature of the ground below the frost line (about 3 to 5 feet below the surface) remains at a nearly constant temperature, generally in the 45 Â° -50 Â° F range in northern latitudes, and in the 50 Â° -70 Â° F range in the south.