Fertilising guide

How to fertilise African Blue Basil (Ocimum kilimandscharicum × basilicum 'Dark Opal')— schedule & NPK

Also called Perennial Basil.

More about african blue basil

About African Blue Basil

Ocimum kilimandscharicum × basilicum 'Dark Opal' · also called Perennial Basil · herb

African Blue basil is a sterile interspecific hybrid that is unusually long-lived and vigorous, with camphor-scented purple-veined leaves and near-constant lavender flower spikes that are magnets for bees. Because it sets no seed it never truly bolts, so it stays productive for months. Tender to frost, it is often overwintered indoors as a perennial.

Growth habit: Large, shrubby, vigorous perennial-in-warmth that flowers almost continuously. Being sterile it never sets seed, so it keeps producing leaves; benefits from periodic hard pinching to stay bushy.

What fertiliser african blue basil actually wants — and why

African Blue 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 african blue 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 african blue 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 african blue basil:

Feed every 3-4 weeks with a balanced liquid fertiliser at half strength through the growing season. As a long-lived, large plant it appreciates steadier feeding than annual basils, especially in containers. 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 african blue 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 african blue basil

Half strength is a sensible default for african blue 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 african blue basil first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the african blue basil watering schedule.

Signs you are over-feeding african blue basil

Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for african blue 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 african blue 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 african blue basil care brief covers soil, humidity and the common problems for this species.

Flushing and leaching the salts

Pot-grown african blue 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 african blue 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 african blue basil — frequently asked questions

What fertiliser does african blue 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. African Blue 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 african blue basil?

Feed every 3-4 weeks with a balanced liquid fertiliser at half strength through the growing season. As a long-lived, large plant it appreciates steadier feeding than annual basils, especially in containers. Feed every 3-4 weeks with a balanced liquid fertiliser at half strength through the growing season. As a long-lived, large plant it appreciates steadier feeding than annual basils, especially in containers. 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 african blue basil?