Cold hardiness & minimum temperature

Is 'January King' Cabbage (Brassica oleracea var. capitata 'January King')cold hardy? Hardiness zone & min temp

Also called January King winter cabbage.

More about 'january king' cabbage

About 'January King' Cabbage

Brassica oleracea var. capitata 'January King' · also called January King winter cabbage · edible

January King is a classic, extremely hardy winter cabbage forming a dense, drum-shaped head with crinkled blue-green outer leaves flushed purple-red in cold. Sown in late spring, it stands in the ground through autumn and winter to harvest from late autumn into late winter. It needs full sun, firm fertile soil and a long, cool season, rewarding patience with a sweet, frost-kissed head.

Cold limit: USDA 6-9 (overwinters in the ground; hardy to around -10°C) · RHS H5 (7-24°C)

Watch for — Pigeon damage: Wood pigeons strip leaves of overwintering cabbages in hard weather. Net or cage plants through autumn and winter to protect them.

What 'january king' cabbage's hardiness rating actually means

Yes — 'january king' cabbage is genuinely cold hardy. Rated RHS H5 and USDA 6-9 (overwinters in the ground; hardy to around -10°C), it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H5 means: Hardy in most of the UK and in cold winters. On the US scale that maps to USDA 6-9 (overwinters in the ground; hardy to around -10°C) — 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

Minimum survivable temperature is roughly about −15 to −10 °C. 'January King' Cabbage is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for 'january king' cabbage as it gets too cold:

It tolerates winter lows to about −15 to −10 °C once established.
Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root.
First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.

Can 'january king' cabbage go outside or overwinter — and where?

Plant it out within USDA 6-9 (overwinters in the ground; hardy to around -10°C) and it overwinters with little or no help.
It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy.
The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

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 'january king' cabbage can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

'January King' Cabbage hardiness — frequently asked questions

Is 'january king' cabbage cold hardy?

Yes — 'january king' cabbage is genuinely cold hardy. Rated RHS H5 and USDA 6-9 (overwinters in the ground; hardy to around -10°C), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. 'January King' Cabbage is hardy across USDA 6-9 (overwinters in the ground; hardy to around -10°C); it belongs in the ground or a frost-proof container, not on a windowsill, and many types actively need a cold winter to perform.

What is the minimum temperature 'january king' cabbage can survive?

Minimum survivable temperature is roughly about −15 to −10 °C. 'January King' Cabbage is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is 'january king' cabbage?

'January King' Cabbage is rated USDA 6-9 (overwinters in the ground; hardy to around -10°C) and RHS H5 — Hardy in most of the UK and in cold winters.

Can 'january king' cabbage survive winter outside?

Plant it out within USDA 6-9 (overwinters in the ground; hardy to around -10°C) and it overwinters with little or no help. It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy. The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

What happens to 'january king' cabbage below its minimum temperature?

It tolerates winter lows to about −15 to −10 °C once established. Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root. First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.