Basil (Ocimum basilicum) adds pungent flavor to your favorite meal and lush, scented greenery to a favorite corner in your garden. The herb thrives as a perennial shrub in U.S. Department of Agriculture plant hardiness zones 10 and higher, or as an annual anywhere else. Instead of buying a started plant from a garden store or nursery, save money by simply rooting a cut stem from an existing plant.
Taking Your Cut
For optimal results, your cutting should come from a vigorously growing outdoor basil plant. While using a piece of cut basil from your grocery store's produce section may occasionally work, these cuttings are often not fresh enough and too dehydrated to take root. Even indoor-grown basil plants are typically too weak to provide a healthy cutting. Instead, wipe down a pair of pruning shears with rubbing alcohol -- this disinfects the shears and prevents the spread of plant diseases -- and snip 4 inches off of the growing tip of a healthy basil branch. Make the cut right below a spot where the basil leaves attach to the stem; this is where the cut piece has the best chance of growing roots.
Option One: Rooting Your Cutting in Water
Pluck off the leaves on the bottom two-thirds of the basil stem, otherwise the leaves will rot when they're under water. Place your basil cutting into a very small cup or jar. The jar should be shallow enough that a third of the basil cutting extends out of the cup, allowing your basil to breathe properly. Fill the jar with water and place it in a sunny location, such as on an east- or west-facing windowsill. Change the water once a day to prevent bacteria build-up. You should see roots developing within a week or two.
Option Two: Rooting Your Cutting in Potting Mix
Use an 8- or 10-inch pot with drainage holes on the bottom. Fill the pot with a sterile, soilless potting mix, such as one made with vermiculite or perlite. Strip off the leaves on the bottom third of the cut basil stem. Dip the cut end of the stem in a rooting hormone powder; though not absolutely necessary, this can increase how quickly the cutting takes root. Use a pencil to poke a hole in the potting mix deep enough for a third of the length of your piece of basil. Insert the cut end of the basil stem into the potting mix and tap down the soil around it. Mist the pot with water to moisten the top few inches of potting medium. Place the pot on a sunny east- or west-facing windowsill. Repeat the watering once or twice a day, or as necessary to keep the cutting moist.
Transplanting Your Cutting
Once the roots on your water-born basil plant measure approximately 1/2-inch long, or once your potted basil cutting has grown several inches high, it's ready for transplanting. You can either move your basil into a 1- or 2-gallon pot filled with soilless potting mix, or you can place your basil plant directly in the ground. Whatever method you choose, its final home should receive full sun. If you place your basil outdoors, only do so after the last frost date in your region to avoid frost injuries to your fragile, new basil shrub.