Fertilising guide

How to fertilise Anise hyssop (Agastache foeniculum)— schedule & NPK

Also called blue giant hyssop, fragrant giant hyssop, lavender hyssop.

About Anise hyssop

Agastache foeniculum · also called blue giant hyssop, fragrant giant hyssop · herb

Anise hyssop is a hardy North American mint-family perennial with aniseed-scented leaves and tall purple flower spikes loved by bees. Used in teas and as a pollinator plant. Pet-safe in moderation.

Agastache foeniculum is a short-lived herbaceous perennial in the Lamiaceae native to prairies, dry upland woods and plains of the upper Midwest, Great Plains and into Canada — a true North American native, not a true hyssop.

A lean-soil prairie plant that needs minimal feeding; it self-sows readily and spreads slowly by rhizomes, so excess fertility mainly drives floppy growth rather than more flowers.

Growth habit: Upright clumping perennial

Sources: plants.ces.ncsu.edu, hort.extension.wisc.edu, hgic.clemson.edu

What fertiliser anise hyssop actually wants — and why

Anise hyssop 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 anise hyssop: 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 anise hyssop, 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 anise hyssop:

Light compost in spring. 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 anise hyssop 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 anise hyssop

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

Signs you are over-feeding anise hyssop

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

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 anise hyssop

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

Flushing and leaching the salts

Pot-grown anise hyssop 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 anise hyssop

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 anise hyssop — frequently asked questions

What fertiliser does anise hyssop 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. Anise hyssop 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 anise hyssop?

Light compost in spring. Light compost in spring. 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 anise hyssop?