It's a simple question: if basil a perennial? Well, strictly speaking, most types of basil are annuals. Basil is generally planted in early spring and harvested during the summer months until it is discarded or goes to seed when frost begins to set in. However, with proper care, some basil may survive multiple growing seasons. Although frosts and cold weather will kill all forms of basil, some cultivars can survive winter months in warmer climates, or can be wintered indoors.
African Blue basil, a shrub with a woody stem, is one of the few naturally perennial basil cultivars. Intolerant of cold weather or frosts, African Blue can be kept inside during the winter months with sufficient sunlight and warmth. Unlike other forms of basil, it will not go to seed or die after flowering.
Thai basil, also called Holy basil and Anise basil, is a second perennial cultivar. Native to Southeast Asia, Thai basil thrives in warm, humid climates and will produce leaves and flowers year-round for several years. This cultivar may not survive the winter in colder areas of the country, even indoors, but may still be grown as an annual herb.
The most popular cultivar of basil is Genovese or Sweet basil, which is an annual plant. While this plant is not bred to produce through multiple growing seasons, you can extend the life of the plant by starting seeds indoors before the first frost to give the plant a head-start for the warmer months. Basil plants can even be grown entirely indoors. Pinching off the flowers will encourage plants to produce leaves more abundantly and prevent it from going to seed and dying. When cold weather hits, bring outdoor plants indoors and keep them on a sunny south-facing window, where they may continue to produce for several more weeks.