Cold hardiness & minimum temperature

Is Japanese Catmint (Nepeta subsessilis)cold hardy? Hardiness zone & min temp

Also called Japanese Catmint, Subsessile Catmint.

More about japanese catmint

About Japanese Catmint

Nepeta subsessilis · also called Japanese Catmint, Subsessile Catmint · flowering

Japanese Catmint is a moisture-tolerant species native to shaded streambanks in Japan, producing vivid violet-blue flowers on upright stems in midsummer. Unlike most catmints, it prefers more water and partial shade, making it valuable for shadier borders or damp garden spots. Excellent for attracting bees and butterflies in cooler climates.

Cold limit: USDA 4–8 · RHS H6 (−20°C to 28°C)

What japanese catmint's hardiness rating actually means

Yes — japanese catmint is genuinely cold hardy. Rated RHS H6 and USDA 4–8, 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 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 about −20 to −15 °C. Japanese Catmint is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for japanese catmint 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 japanese catmint 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 japanese catmint can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Japanese Catmint hardiness — frequently asked questions

Is japanese catmint cold hardy?

Yes — japanese catmint is genuinely cold hardy. Rated RHS H6 and USDA 4–8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Japanese Catmint 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 japanese catmint can survive?

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

What hardiness zone is japanese catmint?

Japanese Catmint is rated USDA 4–8 and RHS H6 — Hardy throughout the UK and northern Europe.

Can japanese catmint 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 japanese catmint 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.