Cut a stem 6 to 8 inches long from the knockout rose bush with a sharp knife at a 45-degree angle. Remove any flowers and leaves, leaving the leaves at the top only.
Dip stems in a rooting hormone powder that can be obtained from a flower nursery. Follow directions on label for correct usage procedures.
Place two-thirds of the stem into a pot with potting soil and sand at the bottom for drainage, recommends Rose Magazine. Spray a mist of water on the rose cutting and soil.
Place a plastic bag over the entire pot and tie with twine. Select a place outside with indirect sunlight. Water just enough to keep the soil moist.
Transplant the rooted stem to a permanent garden location in a month when the rose has rooted.