Cold hardiness & minimum temperature

Is Japanese Mazus (Mazus pumilus)cold hardy? Hardiness zone & min temp

Also called Japanese Mazus, Japanese Mazus Pumilus.

More about japanese mazus

About Japanese Mazus

Mazus pumilus · also called Japanese Mazus, Japanese Mazus Pumilus · flowering

A small, mostly annual or short-lived perennial from East Asia, growing to around 8–20 cm in height with small, two-lipped blue-purple flowers produced from late spring through early autumn. Spreads by self-seeding and forms loose low colonies in moist, disturbed soils. Naturalises in lawns and paving joints in temperate gardens. Not individually listed by ASPCA.

Cold limit: USDA 5–9 · RHS H5 (-10–30°C)

What japanese mazus's hardiness rating actually means

Yes — japanese mazus is genuinely cold hardy. Rated RHS H5 and USDA 5–9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H5 means: Hardy in most of the UK and in cold winters. 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 −15 to −10 °C. Japanese Mazus is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for japanese mazus as it gets too cold:

It tolerates winter lows to about −15 to −10 °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 mazus 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 japanese mazus can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Japanese Mazus hardiness — frequently asked questions

Is japanese mazus cold hardy?

Yes — japanese mazus is genuinely cold hardy. Rated RHS H5 and USDA 5–9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Japanese Mazus 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 japanese mazus can survive?

Minimum survivable temperature is roughly about −15 to −10 °C. Japanese Mazus is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is japanese mazus?

Japanese Mazus is rated USDA 5–9 and RHS H5 — Hardy in most of the UK and in cold winters.

Can japanese mazus 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 japanese mazus below its minimum temperature?

It tolerates winter lows to about −15 to −10 °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.