How to grow Thai Basil in New Zealand
Thai basil has glossy green leaves, purple stems and lavender flowers, with a strong anise and liquorice flavour that holds up in curries and stir-fries. It handles warm, humid summers better than Italian basil, which makes it a good choice for Auckland and Northland. Like all basil it is frost tender and loves warmth.
📖 Our full guide: How to Grow Thai Basil in New Zealand
At a glance
When to sow by region
| Region | When to sow | Regional note |
|---|---|---|
| Northland | September to December | |
| Auckland | September to December | |
| Waikato & Bay of Plenty | October to December | Sow from October, once the inland frosts are over in late September. Warm coastal Bay of Plenty gardens can start a few weeks earlier under cover. |
| Central North Island | December | Needs warm nights. Sow in December or grow it under cover. |
| Wellington & Lower North Island | November and December | Needs warm nights. Sow Nov to Dec in a warm spot out of the wind, or grow it under cover. |
| Nelson & Marlborough | November and December | Sow Nov to Dec once the soil is warm; it sulks in cool spring nights. |
| Canterbury | November and December | Frost tender. Sow Nov to Dec once the frosts finish in mid October and the soil warms, or grow it under cover. |
| Otago & Southland | December | Frost tender. Sow in December once the frosts are over, or grow it under cover. |
| Central Otago | December | Frost tender. Sow in December once the frosts are over, or grow it under cover. |
Not to be confused with: Sweet or Genovese basil, the Italian type used for pesto, which has a softer, clove-like flavour and less heat tolerance.
Where to plant
Grow Thai basil in a sunny, sheltered spot in rich, free-draining soil that stays moist. It needs warm nights to grow well, so there is no gain in planting it early into cold soil.
- Northland and Auckland: sow or plant from late September once nights warm up.
- Waikato and the Bay of Plenty: sow from October, once the inland frosts are over.
- Wellington and Nelson: sow in November and December in a warm spot out of the wind, or grow it under cover.
- Central North Island, Otago and Southland: sow in December or grow it in a glasshouse or on a sunny windowsill; in Canterbury, November and December once the soil warms.
Choosing a variety
- Siam Queen is an improved Thai basil with a strong liquorice flavour, glossy leaves and attractive lavender flowers.
- Holy basil (tulsi) is a different species with a spicy, clove-like taste, also used in Thai cooking.
How to plant
- Sow seed in seed-raising mix in a warm spot, barely covered, or sow direct once the soil is warm.
- Plant out or thin seedlings to about 25 cm apart.
- Water in well and mulch to keep the soil moist.
Watering and feeding
Water regularly, at the base of the plant and preferably in the morning, as wet leaves invite disease. Feed weekly with a liquid fertiliser for plenty of leaves.
Pruning and care through the year
- Pinch out the growing tips regularly to keep the plant bushy.
- Pinch off flower spikes to keep leaves coming, or let a few flower for the bees.
- Before autumn frosts, pick the remaining leaves or take cuttings to root on a windowsill.
Harvesting
Pick leaves and tips as needed, taking the tops of stems to encourage branching. Thai basil holds its flavour better in cooking than sweet basil; add it near the end of cooking. Surplus leaves can be frozen.
Growing in pots
Thai basil grows well in a pot or trough of quality potting mix in a sunny, sheltered spot. Keep the mix moist and feed weekly.
Companion planting
Thai basil suits the summer bed with other heat-loving crops.
Good companions
- Tomato Likes the same sun and watering, and its flowers bring in bees.
- Capsicum Another warm-season crop with the same needs.
- Eggplant Shares the hot, sunny bed.
- Chilli Grown and cooked together in Southeast Asian kitchens.
Keep apart
Avoid planting these close to thai basil.
- Sage Sage wants dry, lean soil while basil wants it rich and moist.
- Rue (a bitter, strong-smelling herb that can hold back some plants growing next to it. Its sap can irritate skin)
Pests and diseases
Aphids, whitefly and slugs are the main pests; downy mildew is the main disease in humid weather.
Pests to watch for
- Aphids Small insects on shoot tips and under leaves.
- Whitefly Tiny white insects fly up when the plant is disturbed.
- Slugs and snails (slugs and snails) Seedlings and young leaves eaten overnight.
Diseases to watch for
- Downy mildew Yellowing leaves with grey-purple fuzz underneath in humid weather.
- Fusarium wilt Plants wilt and stems brown from the base. Remove and do not replant basil there.
Common questions
What is the difference between Thai basil and sweet basil?
Thai basil has purple stems, smaller glossy leaves and a strong anise and liquorice flavour that holds up in cooking. Sweet basil has a softer flavour and is the one for pesto.
When should I plant Thai basil?
Once the nights are warm, from late September in the north and November or December further south. Basil sulks in cold soil and is killed by frost.
Should I remove the flowers on Thai basil?
Pinching them off keeps the plant producing leaves. The flowers are pretty and loved by bees, so you can let a few open.
Can I grow Thai basil indoors?
Yes, on a warm, sunny windowsill, which is a good way to extend the season in cooler areas.
Why are my basil leaves going yellow with grey fuzz underneath?
That is downy mildew, common in humid weather. Water at the base in the morning, space plants for air flow, and remove affected plants.
Sources we checked: Yates NZ: How to grow basil; Kings Seeds: Basil Thai Siam Queen; Kings Plant Barn: Herbs grow well guide.