Cold hardiness & minimum temperature

Is Anise hyssop (Agastache foeniculum)cold hardy? Hardiness zone & min temp

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.

Cold limit: USDA 4-8 · RHS H5 (15-26°C)

Watch for — Crown rot in wet winters: Needs sharp drainage.

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

What anise hyssop's hardiness rating actually means

Yes — anise hyssop is genuinely cold hardy. Rated RHS H5 and USDA 4-8, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H5 means: Hardy in most of the UK and in cold winters. On the US scale that maps to USDA 4-8 — the zones where it can be left outdoors year-round.

New to these scales? The USDA hardiness zone map explained covers how the zone numbers work, and you can find your own zone with the zone finder.

Minimum temperature — and what happens below it

Minimum survivable temperature is roughly about −15 to −10 °C. Anise hyssop is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for anise hyssop as it gets too cold:

It tolerates winter lows to about −15 to −10 °C once established.
Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root.
First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.

Can anise hyssop go outside or overwinter — and where?

Plant it out within USDA 4-8 and it overwinters with little or no help.
It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy.
The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

Work back from your local frost dates with the frost-date calculator: the last spring frost and first autumn frost are what really decide when anise hyssop can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Anise hyssop hardiness — frequently asked questions

Is anise hyssop cold hardy?

Yes — anise hyssop is genuinely cold hardy. Rated RHS H5 and USDA 4-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Anise hyssop is hardy across USDA 4-8; it belongs in the ground or a frost-proof container, not on a windowsill, and many types actively need a cold winter to perform.

What is the minimum temperature anise hyssop can survive?

Minimum survivable temperature is roughly about −15 to −10 °C. Anise hyssop is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is anise hyssop?

Anise hyssop is rated USDA 4-8 and RHS H5 — Hardy in most of the UK and in cold winters.

Can anise hyssop survive winter outside?

Plant it out within USDA 4-8 and it overwinters with little or no help. It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy. The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

What happens to anise hyssop below its minimum temperature?

It tolerates winter lows to about −15 to −10 °C once established. Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root. First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.