Can Broccoli and Cauliflower Survive Frost?

The short answer is: broccoli yes, cauliflower it depends. Brassicas as a family are among the most cold-tolerant vegetables, and many are deliberately grown through autumn and winter. But there are real differences between the frost tolerance of broccoli and cauliflower, and between well-established plants and young transplants. Getting the details right means you can extend the season without losing crops to avoidable cold damage.

Broccoli's frost tolerance

Established broccoli plants can tolerate frosts down to about -5°C or -6°C without significant damage. The leaves may look limp and dark after a frost but recover as they warm up. Purple sprouting broccoli in particular is bred for winter hardiness and regularly tolerates temperatures well below freezing in sheltered gardens. Young transplants, however, are more vulnerable and can be killed by a late spring frost in their first few weeks after planting — protect them with fleece until established.

Cauliflower and frost

Cauliflower plants themselves are reasonably frost-hardy but the curds — the harvest-able heads — are much more vulnerable. An unprotected curd exposed to temperatures below -3°C will develop brown, watery discolouration that makes it inedible or greatly reduced in quality. When a frost is forecast and you have cauliflowers with developing curds, either harvest immediately or bend the outer leaves over the curd to insulate it. This traditional technique of blanching also protects from mild frost as well as sunlight.

What frost-damaged brassicas look like

Frost-damaged leaves are dark, water-soaked and limp in the morning after a freezing night. In mild frosts, leaves recover fully as the temperature rises. In hard frosts, damage is permanent — affected leaves turn yellow and die. A frosted cauliflower curd is soft, translucent or brown in the affected areas and deteriorates rapidly. Frost-damaged outer leaves on broccoli can simply be removed if the inner growth is sound.

Protection methods

Horticultural fleece (at least 30g/m² weight) laid directly over plants provides several degrees of frost protection. It allows light and rain through and can be left on for extended periods in cold weather. For cauliflower, bending and tying the outer leaves over the curd is both traditional and effective for protection down to about -3°C.