Cold hardiness & minimum temperature

Is Curly Kale (Brassica oleracea var. sabellica 'Curly Kale')cold hardy? Hardiness zone & min temp

Also called curly kale, Scots kale, common kale.

More about curly kale

About Curly Kale

Brassica oleracea var. sabellica 'Curly Kale' · also called curly kale, Scots kale · edible

Curly kale is a hardy leafy brassica with tightly ruffled, frilly leaves on an upright stem. Exceptionally cold-tolerant, it crops through autumn and winter and actually sweetens after frost. Grow in full sun in firm, fertile, alkaline-leaning soil, keep it well watered and netted against cabbage pests, and pick young leaves over a long season.

Cold limit: USDA 7-10 (overwinters); grown as an annual or biennial in zones 2-11 · RHS H5 (7-24°C)

Watch for — Wind-rock: Tall winter plants loosen in their sockets in gales, tearing roots. Plant firmly and deep, earth up the stems, and stake exposed plants.

What curly kale's hardiness rating actually means

Hardiness works differently for curly kale: 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 H5 means: Hardy in most of the UK and in cold winters. On the US scale that maps to USDA 7-10 (overwinters); grown as an annual or biennial 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 curly kale 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 curly kale 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 curly kale can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Frost protection for borderline curly kale

Curly Kale 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.

Curly Kale hardiness — frequently asked questions

Is curly kale cold hardy?

Hardiness works differently for curly kale: 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. Curly Kale is grown 7-10 (overwinters); grown as an annual or biennial 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 curly kale 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 curly kale?

Curly Kale is rated USDA 7-10 (overwinters); grown as an annual or biennial in zones 2-11 and RHS H5 — Hardy in most of the UK and in cold winters.

Can curly kale 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 curly kale 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.