Thai basil is a perennial herb that grows as a small, multi-branched shrub, reaching up to a foot in height. It has narrow, arrow-shaped leaves that are about half the size of common sweet basil leaves. Thai basil has purple-tinged stems, which offer a nice contrast to the bright green leaves. The leaves are aromatic and have a strong, spicy flavor with hints of licorice. Some varieties have larger leaves, and some have a purple hue. When the plant matures, spikes of lavender and deep purple flowers grow at the tops of the burgundy stems. The flowers share the same intense spice and hint of licorice flavor.
Thai basil stands up to cooking a little better than sweet basil, making it a good choice for soups, stir-fries, and curries. It can also be eaten raw sprinkled over salads or cold noodles dishes, and used interchangeably with sweet basils in most recipes.
Planting and care:
Light requirements: Full sun is ideal, but plants can grow in part shade.
Planting: Space 8 to 18 inches apart, depending on type. (Read the stick tag that comes with the plant for specific spacing recommendations.)
Soil requirements: Plants grow best in rich, moist but well-drained soil with a pH of 6.0 to 7.0. Work organic matter into soil before planting to add fertility and improve moisture retention. In containers, use premium quality potting soil.
Water requirements: Keep soil consistently moist through the growing season. Add a mulch layer to slow water evaporation from soil. In containers, water whenever the top inch of soil is dry.
Frost-fighting plan: Basil is very frost-tender and damaged by temperatures below 40º F. Use a frost blanket to protect newly planted seedlings from late spring frosts or prolong the fall growing season.
Common issues: Pinch flower buds to keep plants from bolting. Once flowers form, leaf flavor changes. Pests to watch out for: aphids, slugs, Japanese beetles, and earwigs. Fungal diseases sometimes occur in humid climates, and root rot is common in poorly drained soil.
Growing tips: Pinch or prune basil plants as they grow to promote branching and bushiness. Never cut into the woody parts of a stem; plants won’t re-sprout.
Harvesting: Pick leaves at any point in the growing season. Choose individual leaves, or snip leafy stems to the length you desire.
Storage: Cut basil stems and place in water like a fresh bouquet. They’ll last for weeks, provided you remove any leaves below the water line and change water regularly. Never place basil in the refrigerator; the cold air damages leaves. Preserve basil by freezing or in herbal vinegar.