Cold hardiness & minimum temperature

Is Sunset Hyssop (Agastache aurantiaca)cold hardy? Hardiness zone & min temp

Also called Sunset Hyssop, Orange Hummingbird Mint, Fragrant Hyssop.

More about sunset hyssop

About Sunset Hyssop

Agastache aurantiaca · also called Sunset Hyssop, Orange Hummingbird Mint · flowering

A compact, floriferous perennial from the mountains of northern Mexico, producing masses of tubular orange to apricot flowers on slender spikes from summer through autumn. Intensely attractive to hummingbirds and bees, with aromatic, mint-scented foliage. Excellent heat and drought tolerance make it ideal for sunny borders, containers, and pollinator gardens.

Cold limit: USDA 6–10 · RHS H3 (−5°C to 38°C)

Watch for — Short-lived in wet, cold winters: Less hardy than A. rugosa; in zones 6–7 with wet winters, plants may not survive without sharp drainage and a dry mulch to protect the crown. Grown as an annual in cooler regions.

What sunset hyssop's hardiness rating actually means

Sunset Hyssop is half-hardy (RHS H3). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Its RHS rating of H3 means: Half-hardy — comes through mild UK winters outside but is killed by a hard freeze. On the US scale that maps to USDA 6–10 — 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 −5 to 1 °C — a light, short frost only. Sunset Hyssop shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for sunset hyssop as it gets too cold:

Down to roughly about −5 to 1 °C it copes, especially if dry and sheltered.
A sustained hard frost collapses the top growth; whether it returns depends on whether the roots, crown or tubers froze.
Wet cold is far more lethal than dry cold for this plant — soggy, frozen soil is the usual killer.

Can sunset hyssop go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 6–10 or a frost-free UK microclimate.
In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter.
A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

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 sunset hyssop can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H3 figure above.

Frost protection for borderline sunset hyssop

Sunset Hyssop is right on a hardiness edge in many gardens, so if you are pushing it, these measures buy it the margin it needs:

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost.
Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse.
Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones.
Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.

Sunset Hyssop hardiness — frequently asked questions

Is sunset hyssop cold hardy?

Sunset Hyssop is half-hardy (RHS H3). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Borderline outdoors. In its mild end of USDA 6–10 (and sheltered UK gardens) sunset hyssop can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature sunset hyssop can survive?

Minimum survivable temperature is roughly about −5 to 1 °C — a light, short frost only. Sunset Hyssop shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is sunset hyssop?

Sunset Hyssop is rated USDA 6–10 and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can sunset hyssop survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 6–10 or a frost-free UK microclimate. In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter. A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

How do I protect sunset hyssop from frost?

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost. Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse. Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones. Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.