How to grow Thai Basil
Updated October 2026
Thai basil is a sweet basil with purple stems, purple flower spikes and a spicy anise-licorice flavor, essential for Thai and Vietnamese cooking such as curries, stir-fries and pho. Like all basil it is a tender annual that loves heat and dies at the first frost, so it is planted after nights warm up in spring. Pinch it often and remove the flowers to keep the leaves coming.
📖 Our full guide: How to Grow Thai Basil
Not to be confused with: Thai basil is a type of sweet basil (Ocimum basilicum). Holy basil, or tulsi, is a different species with a clove-like flavor, and Italian sweet basil lacks Thai basil's anise note.
Where to plant
Grow Thai basil in full sun in fertile soil well supplied with organic matter, and keep it watered. Poor, dry soil gives slow, less flavorful plants. Raised beds and containers help with drainage.
Basil is very sensitive to cold. Cold soil and air stunt it, and leaves blacken and drop when temperatures fall toward 40°F to 50°F, so wait until frost is past and nights stay above about 55°F before planting out.
- Florida: plant from seed in early spring and again in late summer to fall; South Florida can grow it through the cool season. Protect it on cold nights.
- Gulf South and Texas: plant in March and April, and in late summer in the Gulf South.
- Desert Southwest: plant in March and April, and again in September; give afternoon shade in midsummer.
- California: plant from spring into summer.
- Mid-South, Mid-Atlantic and Southern Plains: plant from late April or May into early summer.
- Northeast, Midwest, Northern Plains, Mountain West and the Pacific Northwest: start seed indoors 3 to 4 weeks ahead and plant out in late May or June once the soil is at least 60°F.
- Hawaii: any month. Alaska: grow in a pot or greenhouse in summer.
Choosing a variety
Siam Queen is a robust, aromatic Thai basil variety widely available in the US; Queenette is similar. Look for the purple stems and flower bracts and the anise scent when buying plants.
How to plant
- Sow seed indoors in warm mix, at least 70°F, 3 to 4 weeks before planting out; seeds sprout in about 5 to 7 days. Or sow directly once the soil is warm.
- Cover seed lightly, about 1/4 inch deep, and keep it moist.
- Plant out or thin to about 10 inches apart after the last frost, once nights are above about 55°F.
- Mulch to keep moisture in and weeds down.
Watering and feeding
Keep the soil evenly moist; basil likes regular water, especially in containers and hot weather. Water at the base and in the morning to keep leaves dry.
Feed lightly every few weeks with a balanced fertilizer, or work in compost before planting.
Harvesting
Start harvesting once plants have several sets of leaves. Pinch or snip the growing tips just above a pair of leaves; this keeps the plant compact and branching and extends the harvest. New leaves have the best flavor.
Pinch off the purple flower spikes as they form to keep leaves coming; letting basil flower and set seed shortens its season. Store cut stems in a glass of water on the counter, not in the fridge, which blackens the leaves.
Growing in pots
Thai basil grows well in a pot at least 8 inches wide with a good potting mix, in full sun. Water often, as containers dry out fast in summer.
Using it
Add whole Thai basil leaves at the end of cooking to curries, stir-fries and soups, or serve them fresh with pho, spring rolls and noodle salads. The flowers are edible too.
Propagation and saving seed
Thai basil roots easily from tip cuttings stood in water or moist mix, a handy way to keep a plant going indoors over winter. To save seed, let a few flower spikes ripen, keeping different basil varieties about 150 feet apart to avoid crossing.
Companion planting
Basil suits the warm-season vegetable bed, where it shares the same sun and watering as tomatoes and peppers.
Good companions
- Tomato Likes the same sun and steady watering, and fits between tomato plants.
- Bell Pepper Another warm-season crop with the same watering needs.
- Eggplant Shares the summer bed, sun and watering.
- Chili Pepper A natural partner in the garden and the kitchen.
Keep apart
Avoid planting these close to thai basil.
- Sage Sage likes dry, lean soil, while basil wants regular water and rich soil, so they are hard to grow together.
- Rue Traditionally kept away from basil; it also prefers dry, lean conditions.
Pests and diseases
Basil downy mildew and fusarium wilt are the most serious problems. Aphids, whiteflies and slugs are the common pests.
Pests to watch for
- Aphids Clusters under leaves and on shoot tips.
- Whiteflies Tiny white insects that fly up from under the leaves.
- Slugs and snails Holes in leaves, especially on young plants in damp weather.
Diseases to watch for
- Downy mildew Leaves yellow between the veins with gray-purple fuzz underneath, spreading fast in humid weather. Remove affected plants.
- Fusarium wilt Plants wilt and stems show brown streaks, often one side first. Rotate and use clean seed.
Common questions
What is the difference between Thai basil and regular basil?
Thai basil has purple stems and flowers, smaller, tougher leaves and a spicy anise-licorice flavor that holds up in cooking. Italian sweet basil is milder and softer.
When should I plant Thai basil?
After the last frost, once nights stay above about 55°F. In Florida, plant in early spring and again in late summer or fall. Choose your region at the top of the page for the months.
Should I remove Thai basil flowers?
Yes, if you want leaves. Pinch the flower spikes as they form. Letting the plant flower and set seed shortens its season.
Why are my basil leaves turning black?
Cold is the usual cause: basil leaves blacken in temperatures toward 40°F to 50°F, including in the fridge. Downy mildew can also darken leaves, with gray fuzz underneath.
Can I grow Thai basil indoors?
Yes, in a very bright, warm window or under a grow light. Rooting cuttings in late summer is an easy way to keep a plant over winter.
Sources we checked: UF/IFAS Gardening Solutions: Basil; University of Illinois Extension: Basil.
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