Thai Basil
Worth growing for the aniseed flavour that holds up in a hot wok, but it is greenhouse only in Ireland and slow to start.
Thai basil is a different thing from a Genovese in the kitchen: narrow pointed leaves on purple stems, purple flower spikes, and a strong aniseed and liquorice flavour that survives being cooked rather than vanishing on contact with heat. That is why it goes into curries and stir fries where sweet basil would be pointless. In Ireland it is the least forgiving of the common basils, because it wants real warmth, so treat it as a greenhouse or conservatory plant. Siam Queen is the named selection you will most often find on a packet.
Quick facts
- Botanical name
- Ocimum basilicum
- Type
- Open pollinated
- Category
- Thai or anise basil
- Difficulty
- Challenging
- Hardiness
- Tender, no frost tolerance
- In Ireland
- Needs a greenhouse or tunnel
- Germination
- 5 to 14 days at 18 to 25C
- Sowing depth
- 5mm
- Spacing
- 20cm apart, 25cm between rows
- Height
- 45cm
- Position
- Full sun
- Containers
- Grows well in pots
- Sowing to harvest
- 8 to 12 weeks
- Harvest
- July to October
Sowing and harvest calendar for Thai Basil
Months shaded below are the reliable windows for Irish conditions.
Where to buy Thai Basil basil seeds in Ireland
Irish suppliers that stock this, so postage stays domestic and seed arrives in time to sow. These are plain links, not paid placements.
Garden centres and mixed retailers
- Mr Middleton Irish Six basil varieties, the widest choice here Mail order arm of a long established Mary Street shop, carries the familiar named varieties the organic specialists skip. Visit Mr Middleton , Co. Dublin
- Johnstown Garden Centre Irish Four basil lines including organic Third generation family business near Naas with the widest branded range, though popular varieties sell out by midsummer. Visit Johnstown Garden Centre , Co. Kildare
Why it suits Ireland
It suits Irish kitchens rather than Irish weather. There is no substitute for it in a green curry or a stir fry, and it is not always easy to buy fresh here, which is a better reason to grow something than most.
Under glass it works. In a polytunnel bed or a large pot in a conservatory it reaches around 45cm and crops from July into October. Outdoors it is a waste of seed, more so than sweet basil, because it needs warmer nights to grow at all.
Set expectations on timing. Sown in April it will be slower off the mark than a Genovese sown the same day, and you should not read that as a problem with the seed.
Growing notes
Sow from March to May at 20 to 25C, with a heated propagator if you have one. Germination is slower and less even than sweet basil and can take up to a fortnight.
Pot on into 9cm pots at the first true leaves and move into a 20cm pot or a greenhouse border in late May or June, at 20cm spacing. Keep it in the warmest part of the greenhouse.
Cut whole stems back to a leaf pair from when the plant is 20cm tall. It branches well and responds to hard cutting better than a Genovese does.
The purple flower spikes are handsome and the plant is a good bee plant if you let it flower, but leaf production drops away once it does, so pinch them out unless you have more basil than you can use.
Water in the morning, at the compost, only when the top of the pot has dried. Cool wet compost stalls this variety faster than any other basil on this site.
Common questions
How is Thai basil different from sweet basil?
Flavour and behaviour in the pan. Thai basil is dominated by anethole, the compound that gives aniseed and fennel their character, so it tastes of liquorice rather than clove and sweetness. More usefully, that flavour survives heat, where sweet basil largely disappears if you cook it, which is why Thai basil is added to a curry during cooking and sweet basil is added to pasta at the end. The plant also looks different: narrower leaves, dark purple stems and purple flower spikes.
Can I substitute sweet basil in a Thai recipe?
Not really, and it is worth knowing that before you sow. Sweet basil in a green curry gives you a vague herby note rather than the aniseed lift the dish is built around. If you cannot grow Thai basil, a small amount of fennel frond or a star anise pod gets closer to the intended flavour than Genovese does.
Does it need more heat than other basils?
Yes, and this is the practical Irish problem with it. It is slower to germinate, slower to establish, and more inclined to stall in cool conditions than a Genovese. A greenhouse, polytunnel or conservatory is realistic here; a kitchen windowsill can work if it is south facing and the room is warm at night. An outdoor Irish border is not worth attempting.
More basil to consider
Sweet Genovese
Open pollinated / Sweet basil, large leaved
The pesto basil, and the one worth the extra fuss, but only if you have a greenhouse or a genuinely sunny south facing sill.
Growing notes and stockistsGreek Basil
Open pollinated / Bush basil, small leaved
The basil to start with if you have failed with basil before. Small leaves, dense growth, and far more tolerant of cool damp air.
Growing notes and stockistsDark Opal
Open pollinated / Purple leaved sweet basil
Grown for the colour more than the harvest. Slower and fussier than green basil, so give it the warmest brightest spot you have.
Growing notes and stockists