Fertilising guide
How to fertilise Thai Basil (Ocimum basilicum 'Thai')— schedule & NPK
Also called Thai Basil, Asian Basil, Cinnamon Basil.
More about thai basil
About Thai Basil
Ocimum basilicum 'Thai' · also called Thai Basil, Asian Basil · herb
Thai Basil is a compact, aromatic culinary herb with glossy, slightly serrated leaves and purple stems. It thrives in warm, sunny spots and is prized for its anise-clove scent. Regular harvesting keeps plants bushy and productive. Pinch flowers promptly to extend the harvest season and maintain leaf flavor.
Growth habit: Upright, bushy annual herb; purple-tinged stems with a more compact, slower-bolting habit than sweet basil
What fertiliser thai basil actually wants — and why
Thai Basil is a soft, fast leafy herb that you harvest hard — a modest balanced feed keeps tender growth coming without tipping it into bland or bolting.
A balanced general feed (even N-P-K) at modest strength — enough nitrogen to keep replacing the leaves you pick, but not so much that flavour thins or it bolts to seed.
For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for thai basil: match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.
How often to feed thai basil, and which months
Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For thai basil:
Apply a balanced liquid fertiliser (e.g. 10-10-10 NPK) diluted to half strength every 3–4 weeks during active growth. Avoid high-nitrogen feeds once plants are established, as excessive nitrogen reduces essential oil concentration and flavor. In practice: a balanced liquid feed every few weeks through the main growing and harvesting season (spring through early autumn), more often the harder you are picking it.
The dormant-season rule matters more than the exact interval: skip feeding entirely when thai basil is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.
What strength to mix for thai basil
Half strength is a sensible default for thai basil — enough to fuel regrowth after cutting, gentle enough that the leaves stay aromatic rather than watery.
Feeding always goes onto already-damp soil, never dry roots — water thai basil first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the thai basil watering schedule.
Signs you are over-feeding thai basil
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for thai basil:
- Fast, soft, pale growth with diluted, less aromatic flavour.
- Early bolting (running to flower) and a bitter edge.
- Salt crust and scorched tips on container plants.
Signs you are under-feeding thai basil
- Pale, slow regrowth after cutting and small leaves.
- A tired, stalled plant that cannot keep up with harvesting.
- Yellowing older leaves in a long-spent pot.
If the symptoms point at watering, light or roots rather than nutrition, the full thai basil care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Pot-grown thai basil builds up feed salts quickly — water until it drains each time and flush the pot with plain water every few weeks, especially on a sunny windowsill.
Organic vs synthetic feeds for thai basil
Organic options
A diluted seaweed feed or worm-casting tea keeps soft growth coming without overdoing it. UK: dilute seaweed or Westland; US: Espoma Garden-tone or Neptune's Harvest. Gentle, hard to overdo, flavour-friendly.
Synthetic / liquid feeds
A balanced liquid feed at half strength through harvesting — UK: Phostrogen, Baby Bio or Westland; US: Miracle-Gro all-purpose at half strength. Fast regrowth; just do not overdo the nitrogen.
Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.
Fertilising thai basil — frequently asked questions
What fertiliser does thai basil need?
A balanced general feed (even N-P-K) at modest strength — enough nitrogen to keep replacing the leaves you pick, but not so much that flavour thins or it bolts to seed. Thai Basil is a soft, fast leafy herb that you harvest hard — a modest balanced feed keeps tender growth coming without tipping it into bland or bolting.
How often should I feed thai basil?
Apply a balanced liquid fertiliser (e.g. 10-10-10 NPK) diluted to half strength every 3–4 weeks during active growth. Avoid high-nitrogen feeds once plants are established, as excessive nitrogen reduces essential oil concentration and flavor. Apply a balanced liquid fertiliser (e.g. 10-10-10 NPK) diluted to half strength every 3–4 weeks during active growth. Avoid high-nitrogen feeds once plants are established, as excessive nitrogen reduces essential oil concentration and flavor. In practice: a balanced liquid feed every few weeks through the main growing and harvesting season (spring through early autumn), more often the harder you are picking it.
What strength of feed for thai basil?
Half strength is a sensible default for thai basil — enough to fuel regrowth after cutting, gentle enough that the leaves stay aromatic rather than watery.
What does over-feeding thai basil look like?
Fast, soft, pale growth with diluted, less aromatic flavour. Early bolting (running to flower) and a bitter edge. Salt crust and scorched tips on container plants. Over-feeding thai basil with strong nitrogen is the usual mistake — it grows fast and lush but the leaves turn bland and it bolts to flower sooner, ending the useful harvest early.
Should I flush the soil of thai basil?
Pot-grown thai basil builds up feed salts quickly — water until it drains each time and flush the pot with plain water every few weeks, especially on a sunny windowsill.
Keep reading
- Thai Basil care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water thai basil — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
- How to fertilise pelargonium 'fragrans variegatum'
- How to fertilise pelargonium capitatum
- How to fertilise pelargonium 'clorinda'
- All 6887 fertilising guides in the Growli library