1. Prepare containers first. Use cleanpots or flats with drainage holes. Fill them with a half-and-half mixture of perlite and peat moss, or with perlite or vermiculite alone. Dampen the mixture.
2. Gather cuttings early in the day, when plants are fresh and full of moisture. The parent plant should be healthy and growing vigorously. With a sharp knife or bypass pruners, cut off an 8- to 12-inch length of stem.
Prepare the cuttings by removing and discarding any flower buds, flowers, and side shoots. Then slice the stem into 3- to 4-inch pieces, each with at least two nodes (growing points). Make each cut just below a node, since new roots will form at this point. Strip the lower leaves from each cutting.
3. Dip the cut end in rooting hormone powder, if desired. (Many kinds of plants will root without the use of hormones.) Tap off excess powder.
Using the end of a sharp pencil, make holes in the rooting medium an inch or two apart; then insert the cuttings. Firm the medium around the cuttings and water with a fine spray. Label each container with the name of the plant and the date. Set containers in a warm spot that's shaded but not dark.
Enclose each container in a plastic bag, fastening the bag closed to maintain humidity. Open the bag for a few minutes every day to provide ventilation.
4. Once the cuttings have taken hold and are growing roots, they will begin to send out new leaves. To test for rooting, gently pull on a cutting; if you feel resistance, roots are forming. At this point, expose the cuttings to drier air by opening the bags; if the cuttings wilt, close the bags again for a few days.
When the plants seem acclimated to open air, transplant each to its own pot of lightweight potting soil. By the next planting season, the new plants should be ready to go out in the garden.