Cold hardiness & minimum temperature

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

Also called curly kale, Tuscan kale, cavolo nero, Lacinato kale.

About Kale

Brassica oleracea var. sabellica · also called curly kale, Tuscan kale · edible

Kale is a cold-hardy leafy brassica that crops from late summer through deep winter and into the following spring. Frost sweetens the leaves. Pair with brassica-friendly companions and protect from cabbage white butterflies. Toxic to pets in large amounts.

Kale is the non-heading (Acephala Group) form of Brassica oleracea, the same species as cabbage and broccoli, derived from wild cabbage of the eastern Mediterranean and Asia Minor and grown as a leafy crop since Greek and Roman times.

A hardy biennial grown as an annual that forms a loose leafy rosette rather than a head, tolerates frost down to roughly 25 F, and turns noticeably sweeter after a hard frost converts starches to sugars.

Cold limit: USDA 3-9 · RHS H6 (7-24°C)

Sources: gardens.duke.edu, plants.ces.ncsu.edu, pmc.ncbi.nlm.nih.gov

What kale's hardiness rating actually means

Hardiness works differently for 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 H6 means: Hardy throughout the UK and northern Europe. On the US scale that maps to USDA 3-9 — 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

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

Frost protection for borderline kale

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.

Kale hardiness — frequently asked questions

Is kale cold hardy?

Hardiness works differently for 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. Kale is grown as an annual in USDA 3-9; you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature 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 kale?

Kale is rated USDA 3-9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can 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 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.