Propagate cuttings from new growth in spring or early fall. Cut 3- to 4-inch stems using a sharp pruner, a knife, or shears. Make the cut at an angle just below a node (where a leaf emerges from the stem). Pinch off the bottom leaves and any flowers or buds.
Dip cut ends in a rooting hormone powder to help them grow. Stand cuttings 1 inch deep in a loose sterile soil or soilless mix in the cells of seedling flats or in individual pots.
Cover the plantings with a sheet of plastic or a dome to help keep the soil moist; prop open the cover to let air circulate among the cuttings. Place the cuttings in bright light but out of direct sunlight. In four to six weeks, transfer them to 6-inch pots or transplant them in the garden.
Note: You can also root cuttings in a glass of water set on a sunny windowsill. Periodically add fresh water and replace it if it looks cloudy. Plant well-rooted cuttings in soil.