Thai basil: profile, planting & care

Thai basil is one of the most popular varieties of sweet basil and has a distinctive anise flavour. Find out everything you need to know about growing and harvesting this delicious herb!

Native to Southeast Asia and popular in local cuisine, Thai basil (Ocimum basilicum var. thyrsiflora) has grown in popularity across much of Europe. Despite its tropical origins, it is easy to grow Thai basil at home as it thrives even in temperate climates.

Thai basil: origin and characteristics

As with all Ocimum basilicum varieties, Thai basil is native to the tropics of Asia. Its anise flavour lends itself to the cuisines of the region and is quite distinct from the flavour profile of sweet basil. The Ocimum genus belongs to the plant family Lamiaceae, or mint family, which are often aromatic plants. Basil plants are no exception. Thai basil is just one of over 40 cultivars of sweet basil with each offering differences in scent, flavour and colour.

Thai basil is a sturdy, compact, tender perennial which is often grown as an annual. It has a deep purple, square stem and can reach up to 50cm high. The leaves are dark green in colour with a purplish tinge. Rubbing Thai basil leaves between your fingers releases their recognisable anise fragrance.

Thai basil flowers between June and August, during which time the plant produces purple to pink lipped flowers with yellow stamens. The flowers form a special inflorescence called a thyrsus, from which Thai basil gets its botanical name. Thai basil flowers attract bees and other beneficial insects. After flowering, the plant develops small fruits of around 2mm which contain the seeds.

Is Thai basil a perennial? Yes, Thai basil is a perennial. However, it is neither long-lived nor hardy and must be overwintered properly. In temperate climates it is more commonly grown as an annual.

Planting Thai basil

Location: Thai basil requires a sunny location that is sheltered from the wind and rain. This herb makes a perfect container plant as it can be placed on a sunny windowsill and protected from the elements during cold spells.

Substrates: For planting, a low-nutrient compost such as our Plantura Organic Herb & Seedling Compost will encourage the young plants to develop strong roots. Once the plant is bigger, an all-purpose compost such as our Plantura Organic All Purpose Compost is ideal for providing more nutrients for a healthy, bushy plant growth.

Sowing Thai basil step-by-step:

1. Start the seeds indoors in March or April or sow outdoors from around mid-May if there is no risk of frost.
2. Fill a planting tray with compost and scatter the seeds on top. Lightly press everything down, but ensure the seeds are not covered as they require light to germinate.
3. Place the tray in a warm, sunny place where the temperature remains between 15 to 20°C. Keep the soil evenly moist. Thai basil seeds germinate in around 14 days.
4. Once the seedlings have several true leaves, replant them in nutrient rich soil.

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Planting Thai basil step-by-step:

1. Plant Thai basil plants outdoors in mid-May, after the last frost has passed.
2. If planting in a pot, make sure the pot is at least a third larger than the plant.
3. Fill the bottom of the pot with a layer of drainage material such as terracotta shards or pebbles to avoid waterlogged soil.
4. Add a nutrient-rich, humus-rich, moist, but well-drained soil. It is particularly important that it is not prone to waterlogging.
5. Insert the plant, ensuring the root ball is covered with soil, then compact the soil around the plant and water it.
6. If planting directly outdoors, or in larger planting containers or troughs, it is important to give the plants enough space. A planting distance of 20cm is optimal.

Plant care

Fertilising your Thai basil plant regularly during the growing season will ensure it is supplied with sufficient nutrients. Fertilise Thai basil grown outdoors once every four weeks. Thai basil plants grown in pots require weekly fertilising. Meeting the high nitrogen demands of Thai basil will ensure your plant grows large, lush green leaves. Our Plantura Liquid Flower Food is an excellent choice as you can simply add it to the water when watering your Thai basil, and it is absorbed quickly.

Alternatively, you can mix an organic slow-release fertiliser into the soil before planting the Thai basil. Our Plantura All Purpose Plant Food provides a steady supply of nutrients over a three-month period.

Thai basil likes to be kept moist, so avoid letting the soil dry out completely. Thai basil grown in a pot requires more frequent watering than when grown in the ground. However, make sure the pots have drainage holes to avoid waterlogged soil. When watering, avoid wetting the leaves and do not use cold water.

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Regular harvesting is an important part of Thai basil plant care as it promotes bushy growth and encourages new shoots to form. Additional pruning is not required. Just remove any dry or wilted parts by hand.

Is Thai basil winter hardy?

No, Thai basil is not winter hardy. If growing Thai basil as a perennial, you must overwinter your plant properly. Thai basil will stop growing at temperatures below 15°C. It is easy to overwinter Thai basil grown in pots by simply bringing the plant to a warm and light spot, such as a windowsill or conservatory.

How to propagate Thai basil

It is easy to propagate Thai basil from seeds or cuttings. Seeds can be harvested just before the first frost, dried, stored and sown the following spring as described above.

To propagate Thai basil from cuttings, select young, healthy shoots that have not yet flowered and cut them to around 10cm in length. Remove any foliage from the lower half and place in a glass of water. Remember to change the water regularly. After 14 days, your cutting should have already rooted and can be planted into a substrate.

Harvesting and preserving Thai basil

When cooking with Thai basil, it is best to use it soon after harvesting when it is fresh. If you want to preserve Thai basil, freezing is your best option.

Harvesting Thai basil

Thai basil can be harvested from May through to September. It is important to cut the whole shoot at around 3 to 4cm above ground, just over a pair of leaves, rather than simply plucking single leaves. This will encourage two new shoots to grow from each leaf axil. It is best to use Thai basil leaves when they are as fresh as possible, because they quickly lose a lot of their flavour.

Freezing Thai basil

If you have wondered whether you can freeze Thai basil, the answer is yes. Freezing it is a great way to store the leaves for longer. Do not wash it before freezing as this will wash away some of the flavour. Pluck the leaves from the harvested stems and place in a freezer bag or jar. The leaves can be stored this way for up to three months, after which time they will begin to lose their potency. Another way to preserve Thai basil is to use it to make pesto or herb butter.

Thai basil uses

Thai basil is rarely used as a medicinal plant, but like sweet basil it is said to help with upset stomachs. Its main use is in the kitchen. Common in the cuisines of southern and south-eastern Asia, this herb gives a spicy, fresh, anise flavour to a dish. Thai basil is also commonly used in place of Holy basil (Ocimum tenuiflorum) in western cooking. Whilst it is considerably more robust than sweet basil, Thai basil is only added at the end of cooking and cooked briefly. It can also be added to finished dishes as a garnish or raw in salads. Thai basil is complemented by other spices and herbs such as ginger, galangal, and coriander.