Cold hardiness & minimum temperature

Is Watermint (Mentha aquatica)cold hardy? Hardiness zone & min temp

Also called watermint, water mint, wild mint.

More about watermint

About Watermint

Mentha aquatica · also called watermint, water mint · herb

Watermint is a vigorous native marginal mint of pond edges, ditches and damp ground, with strongly aromatic toothed leaves and rounded lilac flower clusters loved by bees. It thrives in permanently wet or boggy soil and tolerates standing water, spreading fast by runners. Unlike most herbs, it relishes shade and constant moisture, but it is toxic to pets.

Cold limit: USDA 5-9 (fully hardy herbaceous perennial; dies back and resprouts in spring) · RHS H7 (10-24°C)

What watermint's hardiness rating actually means

Yes — watermint is genuinely cold hardy. Rated RHS H7 and USDA 5-9 (fully hardy herbaceous perennial; dies back and resprouts in spring), 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 5-9 (fully hardy herbaceous perennial; dies back and resprouts in spring) — 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. Watermint is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for watermint 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 watermint go outside or overwinter — and where?

Plant it out within USDA 5-9 (fully hardy herbaceous perennial; dies back and resprouts in spring) 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 watermint can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Watermint hardiness — frequently asked questions

Is watermint cold hardy?

Yes — watermint is genuinely cold hardy. Rated RHS H7 and USDA 5-9 (fully hardy herbaceous perennial; dies back and resprouts in spring), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Watermint is hardy across USDA 5-9 (fully hardy herbaceous perennial; dies back and resprouts in spring); 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 watermint can survive?

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

What hardiness zone is watermint?

Watermint is rated USDA 5-9 (fully hardy herbaceous perennial; dies back and resprouts in spring) and RHS H7 — Hardy in the severest European continental winters.

Can watermint survive winter outside?

Plant it out within USDA 5-9 (fully hardy herbaceous perennial; dies back and resprouts in spring) 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 watermint 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.