Moisten a quality potting medium with warm water, and mix with your hands to ensure the water is evenly distributed. The soil should leave your hand moist, but not wet, when you squeeze it into a ball -- like a damp sponge. Fill the growing tray with the moistened soil. Poke your finger into the soil to make 3- to 4-inch-deep holes approximately 4 inches apart.
Cut 6- to 8-inch stem cuttings from a healthy buxus shrub in the early spring before new growth starts or in the fall before the shrub goes dormant. Strip the leaves from the bottom 4 inches of the stem cuttings by gripping firmly in one hand and pulling through the fingers of the other hand. Place the cuttings in water until you are ready to plant.
Pour 2 tsp. of rooting hormone onto a paper plate. Dip the stem cuttings into the rooting hormone and shake off the excess. Stick the cuttings into the growing tray. Tamp the dirt down so the cuttings are supported. Make a hoop out of each wire piece and insert the ends into the soil so the wire is above the cuttings and will keep the plastic from resting on the buxus cuttings.. Cover the growing tray with plastic wrap.
Place the growing tray in a bright location out of direct sunlight. Place the heating mat under the tray. Set the temperature of the heating mat to 65 degrees F. Check the cuttings every day to keep the soil moist and remove any diseased cuttings. It can take up to eight weeks before buxus stem cuttings start to form roots.
Tug the top of the stem cuttings, gently, to feel for any resistance. When a root system develops, the cuttings become anchored into the soil and are held fast. Take the plastic off the growing tray as soon as roots start to form. Allow the new buxus plants to grow another month in the growing tray and then transplant them into individual containers. Harden off the new plants before setting them outside in the garden.