Fill a flower pot with soil and wet the soil until it is moist but not soggy.
Cut off a 3-inch long or longer periwinkle stem right above a node to prevent leaving an unsightly stump when the plant heals.
Place the stem cut-side-down in the soil to a depth of 1 inch. Place the cuttings in a sunny window to establish healthy growth.
Water the soil whenever it feels dry. Keep the plant indoors until the next spring season to give it a chance to develop strong roots and foliage.
Transplant the cuttings 6 inches apart in late spring when temperatures are consistently higher than 65 degrees Fahrenheit. Water the plants thoroughly after the initial planting. After they are established, water them only during drought conditions.