Take a 6-inch-long stem cutting from a basil plant. For dwarf basil cultivars, a 4-inch cutting will do.
Fill a tall vase, bottle or glass with room-temperature water.
Place the basil cutting in the glass so the stem floats in the water and the leaves remain dry. Keep the jar in a sunny location.
Refresh the water level to maintain its height, and change out the water once or twice a week to ensure clean water. The basil stem sets new roots in about two weeks, so continue this care and watch for roots forming.
Fill a 4-inch pot halfway with a peat-based soil mix. Place the basil cutting in the pot, then add soil up to 1 inch from the top, to cover the roots and plant the basil. Water the newly planted basil to saturate the soil.
Care for the plant indoors for a couple of weeks, then transplant it into the garden if you wish.