Basil (Ocimum basilicum) is an annual herb that's part of the mint family. It is one of the easiest herbs to grow and you can harvest its leaves all season. Though the flowers may look pretty, you should not allow them to form on the plants if you plan to use the leaves for cooking. After flowering, the basil plant produces fewer leaves and the leaves develop a bitter taste.
To develop the tastiest leaves, grow basil in a sunny spot. At least six hours of sun per day is best. You can sow seeds directly in the ground or plant out seedlings in spring after all danger of frost has passed. Thin the seedlings after they develop true leaves to give the remaining plants plenty of room. Mulch to keep down weeds and conserve moisture. Water during dry spells. Harvest leaves regularly to stimulate further leaf production and discourage flowering.
Because regular harvesting is critical to maintain the best leaf flavor, plant basil in a convenient spot, such as in pots close to the kitchen door. Basil is also a traditional component of large and small herb gardens and purple-leaved varieties can add color to those areas. You can also plant basil in ornamental gardens -- wherever there is a spot in the sun. Small-leaved varieties work well as an edging for either ornamental or vegetable beds.
Different basil varieties have different tastes. Lemon-scented basil (Ocimum x citriodora) bears large leaves with lemony overtones. A sport of this lemon-scented hybrid, "Pesto Perpetuo" (Ocimum x citriodora "Pesto Perpetuo"), is highly ornamental, with white-edged leaves. These hybrids have a columnar habit, but do not flower, so you don't have to worry as much about harvesting. "Purpurescens" opal basil (Ocimum basilicum "Purpurescens") bears attractive purple foliage and pink flowers. "Thai Magic" (Ocimum basilicum "Thai Magic") and other Thai-style basils are spicy and intense, with purple stems and flowers.
Growing a continuous supply of basil means preventing flower formation. As the growing season progresses, the plants usually produce an abundance of leaves. If you can't use all the leaves in cooking, keep harvesting them anyway and preserve them by conventional or microwave drying or freezing. You can dig up the plants in fall and bring them inside to continue harvesting. Indoors, the basil will need supplemental light to continue producing leaves. Harvest regularly until leaf production diminishes. Discard the plant and start with fresh seed in the spring.