An easy-to-grow herb with attractive, bright green leaves, basil (Ocimum basilicum) is a feature in most herb gardens. The versatile, heat-loving herb, which thrives outdoors or indoors on a sunny windowsill, adds pungent flavor and aroma to a variety of dishes. Grown as an annual in most climates, basil is perennial in U.S. Department of Agriculture plant hardiness zones 9 through 11. Cuttings taken from a healthy, mature basil plant root reliably in water.
Spring is the best time to propagate basil because the plants are actively growing. You can also take cuttings in summer, but cuttings taken in late summer or fall when the plant is dormant or near-dormant aren't likely to root. To take cuttings, use a clean, sharp knife or scissors to cut several 3- to 4-inch stem tips, then pinch the leaves from the lower one-half of the stems. Make sure the plant is healthy with no indication of disease or pests. Look for sturdy stems and avoid weak, spindly growth.
Rooting in Water
A glass container with a wide top and narrow bottom works well for rooting basil because you can easily see when roots are growing. Although clear glass works well, a lightly tinted glass container is useful because it protects the cuttings from sun and prevents bacteria from growing in the water. To plant the cuttings, place a piece of wire mesh over the container. Fill the container with tap water, then insert the cuttings through the wire mesh. You can plant several cuttings in the container as long as they aren't crowded. Make sure the leaves are above the water because submerged leaves will cause the stems to rot.
Caring for Cuttings
A sunny kitchen window is a good spot for rooting basil, but a bright window with intense, direct light is too strong. If you don't have a convenient window away from intense light, wrap the container with newspaper to protect the stems from scorching. Change the water at least every other day to prevent growth of bacteria that will rot the stems. Ensure the bottoms of the stems are always submerged. As a general rule, basil cuttings root in two weeks or less.
Basil cuttings are ready to move to containers when the roots are about 1/2 inch long. Don't allow the roots to grow longer than about 1 1/2 inches because the fragile roots become tangled and are likely to break. Separate the stems gently, then plant each rooted stem in a 3-inch container filled with a regular, peat-based commercial potting soil. You can also make your own potting mix by combining equal parts peat moss and perlite or vermiculite. To create the proper soil pH, mix 1/2 teaspoon of horticultural lime in each container. After planting, water the cuttings with a dilute solution water-soluble fertilizer mixed at a rate of 1/4 teaspoon per 1 gallon of water.
Newly planted basil cuttings benefit from a few days in shade while the roots settle into their new home. After about a week, move the pots to a sunny window or place them about 6 inches below a grow light or fluorescent bulb. Water the basil with the diluted fertilizer every fourth or fifth watering. For the best chance of long-term success, let the basil mature several weeks before moving the plants into the garden or into larger pots. If you root basil in early spring, move the plants outdoors in summer. If you start basil in summer, it often works well to grow the plants indoors for the winter, then move them outdoors after all danger of frost has passed the following spring.