Thai Basil

Other common names: Common Basil, Basil, 罗勒, 九层塔

Thai basil is a staple herb in many Southeast Asian gardens, and thrives in tropical climates. Thai basil leaves and flowers are harvested for salads, sauces, soups and stir-fries for many Thai and Vietnamese dishes. The sprouts can also be eaten as microgreens!

Thai basil plants are typically treated as annual crops due to their rapid flowering, but they can also be kept as perennials if their flowers are pruned before they can set seed.

Thai basils are part of the Lamiaceae or mint family, which includes other popular herbs like Indian borage, and spearmint.

Sun and soil needs:

Thai basil thrives in 4-6 hours of direct sunlight, but plants can also tolerate about 6-8 hours of indirect sunlight. Plants do best in pots with loamy soil at least 15cm deep, or in true ground. These plants are vulnerable to root rot, so ensure that your pots drain well, and that your soil has plenty of organic matter to let the roots breathe. Keep your plants cool with mulch and plenty of water to encourage growth.

Sowing seeds:

Sow seeds individually in a seedling tray filled with potting mix or seedling mix. Lightly mist the soil until damp, once a day. Seeds should sprout within two weeks.

The seedlings will be vulnerable to high heat and heavy rain and are best kept in a sheltered propagation area or a shaded space with around 4 hours of partial or direct sunlight.

Seeds can also be sown directly into pots or the ground around 15cm apart. Lightly water the soil until damp, once a day. Seeds should sprout within a week.

Transplanting:

Seedlings will be ready for transplanting into pots or true ground when they are roughly 10cm tall. Leave 15cm between each plant to encourage more growth and better ventilation.

Growing:

Thai Basil plants grow rapidly, especially with regular harvesting. The use of high nitrogen fertilisers will encourage the plant to grow more leaves. Plants can be fertilised once a month after transplanting, or after hard pruning.

Thai basil plants will die after setting seed. Prolong your harvest by pinching off flowers when they appear.

Harvesting:

Plants can be harvested for leaves at any time. They are typically harvested continuously via the cut-and-come-again method. Regular harvesting via pruning will encourage bushiness and keep the plant productive.

Seeds can be harvested from flowers that have developed into dry, brown seed capsules.

Propagation:

Thai basil can be grown from seed or propagated via stem cuttings rooted in water or soil.

Common problems & solutions:

Like most strong-smelling herbs, this plant is relatively resistant to pests and disease if kept healthy.

Aphids, mealy bugs, whiteflies, and spider mites often infest the plant if it has underlying problems like repeated wilting from heat stress. Mechanical pest control methods like pruning the infested parts are the best methods for managing these pests in the short term, but resolving the underlying problem will prevent them in the long term.

Wilting leaves during hot weather is a sign of heat stress. Increase the number of times the plant is watered daily, and apply mulch at the base to prevent water loss.