Mature size & growth rate

How big does Anise hyssop (Agastache foeniculum) get?

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.

An exceptional pollinator magnet — bees of many genera, plus butterflies, moths and the occasional hummingbird — and deer/rabbit resistant. Easily raised from seed (often blooming year one) and divided in spring or fall.

Mature size: 60-100 cm tall

Watch for — Floppy stems: Cut back by a third in early summer for bushier growth.

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

Indoor size vs how big it gets in the wild

Anise hyssop stays fairly low but widens over time — it spreads into a bigger clump by offsets, runners or rhizomes rather than shooting upward. Indoors and in a pot, expect 60-100 cm tall. A pot, your light levels and a little pruning are what set the final size in a home, far more than the plant's theoretical potential.

Size here is about width, not height: the plant builds an ever-wider clump or sends out plantlets and runners while staying relatively short.

Growth rate and years to mature

Anise hyssop is a moderate grower. Realistically, expect three to six years to reach mature indoor size, gaining a steady amount each growing season. Its feeding profile backs this up: light compost in spring.

Want this turned into the right next pot at the right moment? The pot size calculator and the anise hyssop repotting guide cover when and how much to size up — pot size is one of the biggest levers on how fast anise hyssop grows.

How to keep anise hyssop smaller

You are not stuck with the maximum size. For anise hyssop specifically, these are the levers, in order of impact:

Divide the clump every year or two — splitting anise hyssop is the main way to control its spread and refresh it.
Remove runners, plantlets or offsets as they appear if you want it to stay a single tight clump.
Keep it slightly pot-bound; a snug pot naturally limits how wide the clump can get.

The keep-it-smaller method, step by step

Lift the whole plant. Slide anise hyssop out of its pot in spring when the clump has filled it.
Split the clump. Tease or cut the rootball into two or more sections, each with healthy roots and growth.
Repot one division. Put a single division back in the original pot to reset it to a smaller size; pot or give away the rest.
Remove offsets as they form. Through the year, detach new runners or pups to stop it spreading again.

How to grow anise hyssop bigger or faster

If you want it to fill the space sooner, push the conditions rather than hoping — for anise hyssop the accelerators are:

Give it a wider pot and let the clump fill it — width is exactly how this plant gets bigger.
Good light plus regular feeding maximises offset and runner production.
Leave plantlets and offsets attached and feed through the growing season for the fastest spread.

Light is almost always the ceiling. The anise hyssop light requirements page covers exactly how bright a spot it needs to grow at its potential instead of stalling.

When anise hyssop outgrows the room (or the pot)

"Too big" usually arrives as one of these signs for anise hyssop:

The clump bulging over the pot rim or splitting the pot — the cue to divide, not to find a bigger room.
A dense centre that goes bare or tired while the edges keep spreading.
Runners or offsets escaping across the shelf or into neighbouring pots.

If it is the pot rather than the room, it is a repotting job, not a goodbye — see the anise hyssop repotting guide. If you want more of this plant instead of a bigger one, the anise hyssop propagation guide turns prunings into new plants.

Anise hyssop size — frequently asked questions

How big does anise hyssop get?

Anise hyssop reaches 60-100 cm tall when grown indoors. Size here is about width, not height: the plant builds an ever-wider clump or sends out plantlets and runners while staying relatively short.

Is anise hyssop slow or fast growing?

Anise hyssop is a moderate grower. Expect three to six years to reach mature indoor size, gaining a steady amount each growing season. Anise hyssop stays fairly low but widens over time — it spreads into a bigger clump by offsets, runners or rhizomes rather than shooting upward.

How long does anise hyssop take to reach full size?

Roughly three to six years to reach mature indoor size, gaining a steady amount each growing season. Light, pot size and feeding move that timeline more than anything else.

How do I keep anise hyssop smaller?

Divide the clump every year or two — splitting anise hyssop is the main way to control its spread and refresh it. Remove runners, plantlets or offsets as they appear if you want it to stay a single tight clump. Keep it slightly pot-bound; a snug pot naturally limits how wide the clump can get.

How can I make anise hyssop grow bigger or faster?

Give it a wider pot and let the clump fill it — width is exactly how this plant gets bigger. Good light plus regular feeding maximises offset and runner production. Leave plantlets and offsets attached and feed through the growing season for the fastest spread.