Cold hardiness & minimum temperature

Is Mexican Hyssop (Agastache mexicana)cold hardy? Hardiness zone & min temp

Also called Mexican Hyssop, Mexican Giant Hyssop.

More about mexican hyssop

About Mexican Hyssop

Agastache mexicana · also called Mexican Hyssop, Mexican Giant Hyssop · herb

Mexican hyssop is an aromatic, mint-family perennial with lemon-mint-scented foliage and long-blooming spikes of pink to crimson tubular flowers that draw bees and hummingbirds. Used in Mexican herbal teas (toronjil), it is short-lived but easily renewed, drought-tolerant once established, and needs sharp drainage and full sun to flower and overwinter well.

Cold limit: USDA 7-10 (borderline in zone 7; mulch or grow as an annual in colder areas) · RHS H4 (15-28°C)

Watch for — Winter root rot: Wet, heavy soil over winter is the main killer. Plant in sharply drained ground or raised beds and keep the crown dry; in cold regions overwinter cuttings as insurance.

What mexican hyssop's hardiness rating actually means

Yes — mexican hyssop is genuinely cold hardy. Rated RHS H4 and USDA 7-10 (borderline in zone 7; mulch or grow as an annual in colder areas), it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H4 means: Hardy in an average winter across much of the temperate world. On the US scale that maps to USDA 7-10 (borderline in zone 7; mulch or grow as an annual in colder areas) — 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 −10 to −5 °C. Mexican Hyssop is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for mexican hyssop as it gets too cold:

It tolerates winter lows to about −10 to −5 °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 mexican hyssop go outside or overwinter — and where?

Plant it out within USDA 7-10 (borderline in zone 7; mulch or grow as an annual in colder areas) 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 mexican hyssop can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H4 figure above.

Frost protection for borderline mexican hyssop

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

At the cold edge of its range, mulch the root zone in late autumn to buffer the deepest freezes.
Protect container specimens — pots freeze through far faster than open ground, costing roughly a zone of hardiness.
Shelter new growth from late spring frosts with fleece if a hard night is forecast.

Mexican Hyssop hardiness — frequently asked questions

Is mexican hyssop cold hardy?

Yes — mexican hyssop is genuinely cold hardy. Rated RHS H4 and USDA 7-10 (borderline in zone 7; mulch or grow as an annual in colder areas), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Mexican Hyssop is hardy across USDA 7-10 (borderline in zone 7; mulch or grow as an annual in colder areas); 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 mexican hyssop can survive?

Minimum survivable temperature is roughly about −10 to −5 °C. Mexican Hyssop is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is mexican hyssop?

Mexican Hyssop is rated USDA 7-10 (borderline in zone 7; mulch or grow as an annual in colder areas) and RHS H4 — Hardy in an average winter across much of the temperate world.

Can mexican hyssop survive winter outside?

Plant it out within USDA 7-10 (borderline in zone 7; mulch or grow as an annual in colder areas) 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.

How do I protect mexican hyssop from frost?

At the cold edge of its range, mulch the root zone in late autumn to buffer the deepest freezes. Protect container specimens — pots freeze through far faster than open ground, costing roughly a zone of hardiness. Shelter new growth from late spring frosts with fleece if a hard night is forecast.