Cold hardiness & minimum temperature

Is Mizuna (Brassica rapa var. niposinica)cold hardy? Hardiness zone & min temp

Also called Japanese mustard greens, Spider mustard.

More about mizuna

About Mizuna

Brassica rapa var. niposinica · also called Japanese mustard greens, Spider mustard · edible

Mizuna is a fast, vigorous Japanese salad brassica forming a feathery rosette of deeply serrated, glossy green leaves with a mild peppery-mustard tang. One of the easiest cut-and-come-again greens, it crops in 3-6 weeks, regrows after cutting, and is far slower to bolt than most leafy brassicas. It suits spring, autumn and even winter-protected sowings in cool, moist conditions.

Cold limit: USDA 4-11 (cool-season; hardy to light frost, cropping into winter under cover) · RHS H4 (10-21°C)

What mizuna's hardiness rating actually means

Yes — mizuna is genuinely cold hardy. Rated RHS H4 and USDA 4-11 (cool-season; hardy to light frost, cropping into winter under cover), it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H4 means: Hardy in an average winter across much of the temperate world. On the US scale that maps to USDA 4-11 (cool-season; hardy to light frost, cropping into winter under cover) — 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 −10 to −5 °C. Mizuna is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for mizuna as it gets too cold:

It tolerates winter lows to about −10 to −5 °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 mizuna go outside or overwinter — and where?

Plant it out within USDA 4-11 (cool-season; hardy to light frost, cropping into winter under cover) 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 mizuna can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H4 figure above.

Mizuna hardiness — frequently asked questions

Is mizuna cold hardy?

Yes — mizuna is genuinely cold hardy. Rated RHS H4 and USDA 4-11 (cool-season; hardy to light frost, cropping into winter under cover), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Mizuna is hardy across USDA 4-11 (cool-season; hardy to light frost, cropping into winter under cover); 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 mizuna can survive?

Minimum survivable temperature is roughly about −10 to −5 °C. Mizuna is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is mizuna?

Mizuna is rated USDA 4-11 (cool-season; hardy to light frost, cropping into winter under cover) and RHS H4 — Hardy in an average winter across much of the temperate world.

Can mizuna survive winter outside?

Plant it out within USDA 4-11 (cool-season; hardy to light frost, cropping into winter under cover) 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 mizuna below its minimum temperature?

It tolerates winter lows to about −10 to −5 °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.