Cold hardiness & minimum temperature

Is Clustered Mountain Mint (Pycnanthemum muticum)cold hardy? Hardiness zone & min temp

Also called Clustered mountain mint, Broad-leaved mountain mint, Short-toothed mountain mint.

More about clustered mountain mint

About Clustered Mountain Mint

Pycnanthemum muticum · also called Clustered mountain mint, Broad-leaved mountain mint · herb

Clustered mountain mint is a showy native perennial of moist meadows and forest edges in the eastern United States, notable for its broad silvery-white bracts that surround the flower clusters and give the plant a frosted appearance throughout the long summer bloom period. It is regarded as one of the most valuable native pollinator plants in the eastern US, supporting over 150 bee species. The most important care fact is consistent moisture — it thrives in moderately to consistently moist soils and will struggle in prolonged drought without supplemental water. It is generally regarded as non-toxic to pets.

Cold limit: USDA 4-8 · RHS H7 (-29 to 35°C)

What clustered mountain mint's hardiness rating actually means

Yes — clustered mountain mint is genuinely cold hardy. Rated RHS H7 and USDA 4-8, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H7 means: Hardy in the severest European continental 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 below about −20 °C. Clustered Mountain Mint is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for clustered mountain mint as it gets too cold:

It tolerates winter lows to about −20 °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 clustered mountain mint 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 clustered mountain mint can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Clustered Mountain Mint hardiness — frequently asked questions

Is clustered mountain mint cold hardy?

Yes — clustered mountain mint is genuinely cold hardy. Rated RHS H7 and USDA 4-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Clustered Mountain Mint 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 clustered mountain mint can survive?

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

What hardiness zone is clustered mountain mint?

Clustered Mountain Mint is rated USDA 4-8 and RHS H7 — Hardy in the severest European continental winters.

Can clustered mountain mint 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 clustered mountain mint below its minimum temperature?

It tolerates winter lows to about −20 °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.