Fertilising guide
How to fertilise Korean Mint (Agastache rugosa)— schedule & NPK
Also called Korean mint, blue licorice, wrinkled giant hyssop.
More about korean mint
About Korean Mint
Agastache rugosa · also called Korean mint, blue licorice · herb
Korean mint is an upright, aromatic perennial in the mint family with anise-licorice-scented leaves and tall spikes of purple-blue flowers that draw bees and butterflies. Used as a culinary and medicinal herb across East Asia, it thrives in full sun and well-drained soil, is fairly drought-tolerant once established, and self-seeds readily in the garden.
Growth habit: Upright, clump-forming aromatic perennial that flowers from mid to late summer; self-seeds freely and can be short-lived, persisting via seedlings.
Watch for — Flopping stems: Rich soil, shade or excess feed make stems lax and topple; site in full sun on lean soil for self-supporting growth.
What fertiliser korean mint actually wants — and why
Korean Mint 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 korean mint: 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 korean mint, 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 korean mint:
Undemanding; a single spring application of balanced fertiliser or compost is enough. Over-feeding gives lush, floppy growth and fewer flowers, so keep feeding light. 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 korean mint 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 korean mint
Half strength is a sensible default for korean mint — 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 korean mint first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the korean mint watering schedule.
Signs you are over-feeding korean mint
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for korean mint:
- 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 korean mint
- 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 korean mint care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Pot-grown korean mint 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 korean mint
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 korean mint — frequently asked questions
What fertiliser does korean mint 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. Korean Mint 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 korean mint?
Undemanding; a single spring application of balanced fertiliser or compost is enough. Over-feeding gives lush, floppy growth and fewer flowers, so keep feeding light. Undemanding; a single spring application of balanced fertiliser or compost is enough. Over-feeding gives lush, floppy growth and fewer flowers, so keep feeding light. 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 korean mint?
Half strength is a sensible default for korean mint — enough to fuel regrowth after cutting, gentle enough that the leaves stay aromatic rather than watery.
What does over-feeding korean mint 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 korean mint 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 korean mint?
Pot-grown korean mint 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
- Korean Mint care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water korean mint — 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 basil
- How to fertilise herb garden
- How to fertilise mint
- All 3899 fertilising guides in the Growli library