Fertilising guide

How to fertilise Shiso (Perilla frutescens var. crispa)— schedule & NPK

Also called shiso, perilla, Japanese basil.

More about shiso

About Shiso

Perilla frutescens var. crispa · also called shiso, perilla · herb

Shiso is a fast-growing annual mint relative prized in Japanese, Korean, and Vietnamese cooking for its ruffled green or deep-purple leaves and complex flavour of mint, basil, and anise. It grows easily from seed in warm weather, reaching knee-height in a season, and self-sows readily. Both leaf colours are ornamental as well as edible, thriving in sun to part shade.

Growth habit: Upright, branching, bushy summer annual with square stems and large serrated or ruffled aromatic leaves, producing spikes of tiny flowers in late summer that set abundant self-sowing seed.

What fertiliser shiso actually wants — and why

Shiso 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 shiso: 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 shiso, 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 shiso:

Feed lightly every 3-4 weeks during active growth with a balanced or nitrogen-leaning fertiliser to keep leaf production going, or work compost into the bed at planting. Avoid over-feeding, which can soften flavour. 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 shiso 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 shiso

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

Signs you are over-feeding shiso

Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for shiso:

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 shiso

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 shiso care brief covers soil, humidity and the common problems for this species.

Flushing and leaching the salts

Pot-grown shiso 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 shiso

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 shiso — frequently asked questions

What fertiliser does shiso 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. Shiso 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 shiso?

Feed lightly every 3-4 weeks during active growth with a balanced or nitrogen-leaning fertiliser to keep leaf production going, or work compost into the bed at planting. Avoid over-feeding, which can soften flavour. Feed lightly every 3-4 weeks during active growth with a balanced or nitrogen-leaning fertiliser to keep leaf production going, or work compost into the bed at planting. Avoid over-feeding, which can soften flavour. 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 shiso?