How to grow Thai Basil in Australia
Thai basil (Ocimum basilicum var. thyrsiflora) is a sturdy basil with purple stems, green leaves, purple flower spikes and a sweet anise and clove flavour that holds up in hot curries and stir-fries. It loves heat even more than sweet basil, grows quickly through summer and, in frost-free tropical gardens, can keep going for years.
📖 Our full guide: How to Grow Thai Basil in Australia
At a glance
When to sow by region
| Region | When to sow | Regional note |
|---|---|---|
| South East Queensland | September to March | |
| Northern Rivers NSW | September to March | |
| Sydney & Coastal NSW | September to March | |
| Melbourne & Victoria | October to December | Frost tender. Sow Oct to Dec once nights stay above 10C. Wants more heat than sweet basil, so give it the warmest spot. |
| Adelaide & SA | October to December | Frost tender. Sow Oct to Dec after frost. Grows fast through summer with water; finished by the first May cold. |
| Perth & WA | September to December | Sow Sep to Dec. Give bright shade and steady water from December; it is finished by the first cool nights of May. |
| Tasmania | November and December | Marginal. Even more heat-hungry than sweet basil. Sow Nov to Dec under cover. Greenhouse crop in Tasmania. |
| Canberra & ACT | November and December | Frost tender. Sow Nov to Dec after the last frost in early November; dies at the first autumn frost. |
| North Queensland | April to November | Plant Apr to Nov, as for sweet basil. Thai basil handles heat better, but downy mildew still hits in the monsoon months. |
| Darwin & Top End | All year | Year round in Darwin, as for sweet basil. Thrives in heat and humidity. |
Not to be confused with: Basil (sweet basil), the Italian type with a softer, sweeter flavour. Holy basil (tulsi or krapow) is a different species with a peppery, clove flavour.
Where to plant
Thai basil needs full sun, warmth and rich, well-drained soil with plenty of compost. It stops growing in cool nights and rots in cold, wet soil, so do not plant it out until nights are warm. In very hot, dry areas, light afternoon shade and steady water keep the leaves tender.
It handles heat and humidity better than sweet basil, but downy mildew can still strike in wet, humid weather.
- South East Queensland, the Northern Rivers and Sydney: sow from September to March.
- Melbourne and Adelaide: sow from October to December once nights stay above about 10°C, in the warmest spot. It finishes with the first cold in autumn.
- Perth: sow from September to December. Give it bright shade and steady water from December.
- Canberra: sow in November and December after the last frost. Hobart: marginal, sow in November and December under cover or grow it in a greenhouse.
- North Queensland: plant from April to November. Darwin: grows all year.
How to plant
- Sow seed directly or in punnets once the soil is warm. Cover it very lightly and firm it down.
- Keep the surface moist. Seedlings appear in one to two weeks.
- Plant out or thin seedlings to about 25 to 30 cm apart.
- Or start from cuttings: tip cuttings of Thai basil root easily in a glass of water within a week or two.
Watering and feeding
Keep the soil evenly moist but never waterlogged. Water in the morning at the base of the plant; wet leaves overnight encourage downy mildew.
Feed every couple of weeks with a liquid vegetable and herb fertiliser for steady leafy growth.
Pruning and care through the year
- Pinch out the tips often to keep the plant bushy.
- Pinch off flower spikes as they form. Flowering slows new leaf growth, though the flowers are edible and bees love them; leave a few for the bees if you like.
- Mulch to keep moisture steady through summer.
- In frost-free tropical gardens, cut plants back by about a third when they get leggy to refresh them.
Harvesting
Pick leaves and tips from about eight weeks after sowing. Frequent picking keeps the plant producing. Pick stems just above a pair of leaves so it branches.
Thai basil holds its flavour better in cooking than sweet basil. Store stems in a glass of water on the bench, not in the fridge, where the leaves blacken. Leaves can be frozen or dried for later.
Growing in pots
Thai basil grows well in a pot at least 20 to 25 cm wide with a quality potting mix in full sun. Water often in hot weather and feed regularly.
Using it
Use Thai basil in green and red curries, stir-fries, noodle soups such as pho, fresh spring rolls and salads. Add whole leaves near the end of cooking. The flowers can be used as a garnish.
Cuttings and saving seed
Take 10 cm tip cuttings, strip the lower leaves and stand them in water or moist potting mix; they root quickly in warm weather. To save seed, let a few flower spikes dry on the plant, then rub out the small black seeds and store them dry.
Varieties
- Thai Sweet Basil (Horapa)
- Holy Basil (Krapao)
Companion planting
Thai basil is a natural partner for the summer fruiting crops it is cooked with, and its flowers bring bees to the vegie patch.
Good companions
- Tomato A warm-season crop with the same sun, soil and watering needs.
- Capsicum Shares the warm, rich bed and the same summer season.
- Eggplant Another heat lover for the same bed.
- Chilli Grown and cooked together, with the same warm-season needs.
Keep apart
Avoid planting these close to thai basil.
- Sage Sage wants dry, lean soil while basil wants rich, moist soil. Grow them in different beds.
- Rue Traditionally kept away from basil.
Pests and diseases
Thai basil is fairly tough, but soft growth attracts sap suckers, and downy mildew is a risk in humid weather.
Pests to watch for
- Aphids Clusters under the leaves and on shoot tips.
- Whitefly Tiny white insects flying up from the undersides of the leaves.
- Slugs Holes in young leaves and seedlings eaten off after rain.
- Snails Ragged holes in leaves and slime trails.
Diseases to watch for
- Downy mildew Yellowing between the veins on top of the leaves with grey-purple fuzz underneath, in humid weather.
- Fusarium wilt Plants wilt and yellow even though the soil is moist, with brown streaks inside the stems. Pull out affected plants and do not replant basil there.
Common questions
What is the difference between Thai basil and sweet basil?
Thai basil has purple stems and flower spikes, slightly smaller and firmer leaves, and a stronger anise and clove flavour that holds up in cooking. Sweet basil is softer and sweeter and is used in Italian dishes. They are grown the same way, but Thai basil is a little more heat tolerant.
Is Thai basil the same as holy basil?
No. Holy basil (tulsi or krapow) is a different species with a peppery, clove flavour and slightly hairy leaves. It is the basil used in Thai stir-fried holy basil dishes.
When should I plant Thai basil?
In spring and summer once nights are warm: September to March in South East Queensland and Sydney, October to December in Melbourne and Adelaide. In Darwin it grows all year. Pick your region at the top of the page for the months.
Should I remove Thai basil flowers?
Yes, if you want lots of leaves. Pinch off the flower spikes as they form so the plant keeps producing leaves. The flowers are edible and attract bees, so you can leave a few.
Can I grow Thai basil from cuttings?
Yes, very easily. Stand 10 cm tip cuttings in water or moist mix, and they root within a week or two in warm weather.
Why is my Thai basil going black?
Cold is the usual cause, either cold nights outdoors or storing it in the fridge. Downy mildew can also blacken and yellow the leaves in humid weather. Grow it in warmth and store cut stems in water on the bench.
Sources we checked: Yates: Thai basil seeds; Sustainable Gardening Australia: Basil.