Fertilising guide
How to fertilise Basil (Ocimum basilicum)— schedule & NPK
Also called sweet basil, Genovese basil.
About Basil
Ocimum basilicum · also called sweet basil, Genovese basil · herb
Basil is a fast-growing warm-season annual herb from tropical Asia and the classic Italian kitchen herb. It rewards regular pinching with bushy plants and bolts quickly when stressed. Pet-safe by ASPCA standards.
Sweet basil (Ocimum basilicum) is native to tropical Asia and Africa, including southern Asia and South Pacific islands; that tropical origin makes it acutely cold-sensitive and not winter hardy in temperate gardens.
Responds to fertile soil with bushy growth, but pinching flower buds as they appear is the key intervention that prolongs leaf harvest and keeps the plant productive.
Growth habit: Bushy upright annual
Watch for — Yellow lower leaves: Overwatering, nitrogen depletion, or downy mildew.
Sources: extension.umn.edu, extension.illinois.edu, extension.psu.edu
What fertiliser basil actually wants — and why
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 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 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 basil:
Half-strength balanced liquid feed every 2-3 weeks during the growing season; nothing fancy needed. 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 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 basil
Half strength is a sensible default for 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 basil first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the basil watering schedule.
Signs you are over-feeding basil
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for 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 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 basil care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Pot-grown 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 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 basil — frequently asked questions
What fertiliser does 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. 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 basil?
Half-strength balanced liquid feed every 2-3 weeks during the growing season; nothing fancy needed. Half-strength balanced liquid feed every 2-3 weeks during the growing season; nothing fancy needed. 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 basil?
Half strength is a sensible default for basil — enough to fuel regrowth after cutting, gentle enough that the leaves stay aromatic rather than watery.
What does over-feeding 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 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 basil?
Pot-grown 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
- Basil care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water 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 herb garden
- How to fertilise mint
- How to fertilise rosemary
- All 200 fertilising guides in the Growli library