To speed the germination of seeds and the rooting of some kinds of cuttings, you can convert your cold frame to a hotbed, as shown below.
Making a Hotbed
To convert your cold frame to a hotbed, add an electric heating cable. Make a base for the cable by spreading a 2- to 3-inch layer of sand or vermiculite. Lay the cable, spacing the loops 6 to 8 inches apart and keeping it 3 inches away from the sides of the frame. Add another inch of sand, then a sheet of window screen or hardware cloth to protect the cable. Most growers add another, 4- to 6-inch-thick layer of sand in which to sink pots of plants.