BattenBlooms
PL. —Ocimum basilicum var. thyrsifloraBotanical illustration — drop image
Ocimum basilicum var. thyrsiflora

Thai Basil

SpringSummerFall
2a–11bHardiness zone
Peak bloom windowZone 6b · frost-offset weeks
Winter
Not in bloom
Spring
Peak bloom
Summer
Peak bloom
Fall
Not in bloom
Peak bloom
In bloom
Background

Thai basil has a spicier, anise-forward flavour profile quite different from Genovese basil — it holds up better to heat than Italian types, making it essential for stir-fries, curries, and pho. The purple stems and flowers are ornamental, and unlike sweet basil, the flowers are worth leaving on for decoration and flavour.

Start indoors 6 weeks before last frost. Thai basil is more heat-tolerant than Italian basil and keeps producing through the summer with less bolting. Harvest from the tips to encourage branching; pinch any flower spikes you want to keep as leaf producers.

Good companions
Ocimum basilicumZinnia elegans
Keep apart
Salvia officinalis
Care guide
SunFull sun — 6+ hours
WaterRegular; keep soil moist but not waterlogged
SoilRich, moist, well-draining
Spacing12–18 inches
Height18–24 inches
Zone2a – 11b
WinterAnnual — compost after first frost.
Seasonal tasks
summer
cutPinch stem tips to encourage branching; harvest leaves throughout summer
fall
watchHarvest or bring in before first frost — blackens overnight
Common problems

Downy mildew

Symptoms

Yellowing on top of leaves with grey-purple fuzz underneath. Spreads rapidly in humid conditions.

Treatment

Remove affected leaves. Improve air circulation. Avoid overhead watering. Copper spray as preventive.