Cold hardiness & minimum temperature

Is Cavolo Nero (Brassica oleracea var. palmifolia 'Cavolo Nero')cold hardy? Hardiness zone & min temp

Also called cavolo nero, black kale, Tuscan kale, dinosaur kale.

More about cavolo nero

About Cavolo Nero

Brassica oleracea var. palmifolia 'Cavolo Nero' · also called cavolo nero, black kale · edible

Cavolo nero is an Italian kale with long, narrow, deeply puckered blue-black leaves on an upright palm-like stem. Hardy and slow to bolt, it crops from late summer through winter and sweetens after frost. Grow in full sun in firm, fertile, alkaline-leaning soil, water steadily, net against cabbage pests, and pick leaves from the base.

Cold limit: USDA 7-10 (overwinters); grown as an annual or biennial in zones 2-11 · RHS H4 (7-24°C)

Watch for — Wind-rock: The tall, top-heavy stems rock loose in winter winds, damaging roots. Plant deep and firm, earth up the base, and stake plants on exposed sites.

What cavolo nero's hardiness rating actually means

Hardiness works differently for cavolo nero: 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 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 cavolo nero 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 cavolo nero 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 cavolo nero 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 cavolo nero

Cavolo Nero 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.

Cavolo Nero hardiness — frequently asked questions

Is cavolo nero cold hardy?

Hardiness works differently for cavolo nero: 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. Cavolo Nero 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 cavolo nero 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 cavolo nero?

Cavolo Nero is rated USDA 7-10 (overwinters); grown as an annual or biennial in zones 2-11 and RHS H4 — Hardy in an average winter across much of the temperate world.

Can cavolo nero 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 cavolo nero 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.