Cold hardiness & minimum temperature

Is Horse Mint (Mentha longifolia)cold hardy? Hardiness zone & min temp

Also called Horse Mint, Horsemint, Bible Mint, Long-Leafed Mint.

More about horse mint

About Horse Mint

Mentha longifolia · also called Horse Mint, Horsemint · herb

Horse Mint is a tall, vigorous wild mint native from Europe to Central Asia, recognisable by its grey-green woolly leaves and branching spires of pale lilac to white flowers. More robust and wilder in character than culinary mints, it naturalises in moist, partly shaded spots and spreads freely by rhizome.

Cold limit: USDA 5-9 · RHS H6 (5–25°C)

What horse mint's hardiness rating actually means

Yes — horse mint is genuinely cold hardy. Rated RHS H6 and USDA 5-9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H6 means: Hardy throughout the UK and northern Europe. On the US scale that maps to USDA 5-9 — 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 −20 to −15 °C. Horse Mint is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for horse mint as it gets too cold:

It tolerates winter lows to about −20 to −15 °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 horse mint go outside or overwinter — and where?

Plant it out within USDA 5-9 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 horse mint can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Horse Mint hardiness — frequently asked questions

Is horse mint cold hardy?

Yes — horse mint is genuinely cold hardy. Rated RHS H6 and USDA 5-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Horse Mint is hardy across USDA 5-9; 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 horse mint can survive?

Minimum survivable temperature is roughly about −20 to −15 °C. Horse Mint is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is horse mint?

Horse Mint is rated USDA 5-9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can horse mint survive winter outside?

Plant it out within USDA 5-9 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 horse mint below its minimum temperature?

It tolerates winter lows to about −20 to −15 °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.