Cold hardiness & minimum temperature

Is Mizuna 'Red Kingdom' (Brassica rapa var. nipposinica 'Red Kingdom')cold hardy? Hardiness zone & min temp

Also called Red mizuna, purple mizuna.

More about mizuna 'red kingdom'

About Mizuna 'Red Kingdom'

Brassica rapa var. nipposinica 'Red Kingdom' · also called Red mizuna, purple mizuna · edible

'Red Kingdom' is an F1 red mizuna with deeply serrated purple-red leaves on slim stems, adding colour and a mild mustard bite to salad mixes. Vigorous and slow to bolt, it holds its rich pigment best in cool weather and bright light, regrows well after cutting, and tolerates light frost, making it a standout baby-leaf and stir-fry green.

Cold limit: USDA Grown as a cool-season annual in zones 2-11 · RHS H4 (10-24°C)

What mizuna 'red kingdom''s hardiness rating actually means

Hardiness works differently for mizuna 'red kingdom': it is grown as a seasonal crop, not overwintered. The question is not "what zone" but "how long is your frost-free growing window". 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 Grown as a cool-season annual in zones 2-11 — 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

As an annual crop, its "minimum temperature" is the first hard frost — that is the end of the plant's life, not a survivable low. Many types are also damaged by light frost (around 0 °C).

Concretely, for mizuna 'red kingdom' as it gets too cold:

Light frost (around 0 to −2 °C) damages or kills tender summer crops outright; cold-hardy types take a few degrees of frost.
The plant does not "survive winter" — its life cycle simply ends, by design, when frost arrives or it finishes cropping.
A surprise late spring frost can also kill young transplants set out too early, before the season even starts.

Can mizuna 'red kingdom' go outside or overwinter — and where?

Time it to your frost dates: sow or plant out after the last spring frost, and aim to harvest before the first autumn frost.
In short-season zones, start it indoors or under cover to stretch the effective growing window.
Hardier crops in this group can be sown for an autumn or overwintered harvest in mild zones — check the specific crop.

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 'red kingdom' can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H4 figure above.

Frost protection for borderline mizuna 'red kingdom'

Mizuna 'Red Kingdom' is right on a hardiness edge in many gardens, so if you are pushing it, these measures buy it the margin it needs:

Use fleece, cloches or a cold frame at each end of the season to dodge a borderline frost and add growing weeks.
Have row cover ready for an unexpected late spring or early autumn frost.
Know your local last- and first-frost dates and count back the crop’s days-to-maturity to schedule the sowing.

Mizuna 'Red Kingdom' hardiness — frequently asked questions

Is mizuna 'red kingdom' cold hardy?

Hardiness works differently for mizuna 'red kingdom': it is grown as a seasonal crop, not overwintered. The question is not "what zone" but "how long is your frost-free growing window". A seasonal crop, not a perennial. Mizuna 'Red Kingdom' is grown Grown as a cool-season annual in zones 2-11; you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature mizuna 'red kingdom' can survive?

As an annual crop, its "minimum temperature" is the first hard frost — that is the end of the plant's life, not a survivable low. Many types are also damaged by light frost (around 0 °C).

What hardiness zone is mizuna 'red kingdom'?

Mizuna 'Red Kingdom' is rated USDA Grown as a cool-season annual in zones 2-11 and RHS H4 — Hardy in an average winter across much of the temperate world.

Can mizuna 'red kingdom' survive winter outside?

Time it to your frost dates: sow or plant out after the last spring frost, and aim to harvest before the first autumn frost. In short-season zones, start it indoors or under cover to stretch the effective growing window. Hardier crops in this group can be sown for an autumn or overwintered harvest in mild zones — check the specific crop.

How do I protect mizuna 'red kingdom' from frost?

Use fleece, cloches or a cold frame at each end of the season to dodge a borderline frost and add growing weeks. Have row cover ready for an unexpected late spring or early autumn frost. Know your local last- and first-frost dates and count back the crop’s days-to-maturity to schedule the sowing.