Cold hardiness & minimum temperature

Is Broccoli (Brassica oleracea var. italica)cold hardy? Hardiness zone & min temp

Also called calabrese, sprouting broccoli, purple sprouting broccoli.

About Broccoli

Brassica oleracea var. italica · also called calabrese, sprouting broccoli · edible

Broccoli is a cool-season brassica grown for its tight flower heads. Calabrese types produce one large central head and a flush of side shoots; sprouting types are smaller-headed but crop over a longer period. Toxic to pets in large amounts.

Broccoli is the Italica Group of Brassica oleracea, an Old World Mediterranean cultigen grown for its head of immature, unopened flower buds atop a thick stalk.

Forms a central head of clustered flower buds about 50-70 days after emergence; flowering is influenced by facultative vernalization, and many side shoots produce a secondary harvest after the main head is cut.

Cold limit: USDA 3-9 · RHS H5-H6 (10-21°C)

Watch for — Tiny "buttoning" heads: Cold check on young plants or poor soil; feed and water consistently.

Sources: content.ces.ncsu.edu, gardeningsolutions.ifas.ufl.edu, pmc.ncbi.nlm.nih.gov

What broccoli's hardiness rating actually means

Hardiness works differently for broccoli: 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 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 broccoli 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 broccoli 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 broccoli 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 broccoli

Broccoli 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.

Broccoli hardiness — frequently asked questions

Is broccoli cold hardy?

Hardiness works differently for broccoli: 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. Broccoli 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 broccoli 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 broccoli?

Broccoli is rated USDA 3-9 and RHS H5 — Hardy in most of the UK and in cold winters.

Can broccoli 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 broccoli 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.