Cold hardiness & minimum temperature

Is Autumn Crocus (Colchicum autumnale)cold hardy? Hardiness zone & min temp

Also called Meadow Saffron, Naked Ladies, Dog's Mercury.

More about autumn crocus

About Autumn Crocus

Colchicum autumnale · also called Meadow Saffron, Naked Ladies · flowering

Autumn Crocus is a deceptive European corm that flowers bare in autumn — naked of leaves, which appear separately in spring. It belongs to Colchicaceae and contains colchicine, an extremely potent alkaloid toxic to all animals and humans. Despite its beauty, it is one of the most dangerous garden plants to pets and children.

Cold limit: USDA 4-9 · RHS H7 (2-22°C)

What autumn crocus's hardiness rating actually means

Yes — autumn crocus is genuinely cold hardy. Rated RHS H7 and USDA 4-9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H7 means: Hardy in the severest European continental winters. On the US scale that maps to USDA 4-9 — 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

Minimum survivable temperature is roughly below about −20 °C. Autumn Crocus is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for autumn crocus as it gets too cold:

It tolerates winter lows to about −20 °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 autumn crocus go outside or overwinter — and where?

Plant it out within USDA 4-9 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 autumn crocus can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Autumn Crocus hardiness — frequently asked questions

Is autumn crocus cold hardy?

Yes — autumn crocus is genuinely cold hardy. Rated RHS H7 and USDA 4-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Autumn Crocus is hardy across USDA 4-9; 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 autumn crocus can survive?

Minimum survivable temperature is roughly below about −20 °C. Autumn Crocus is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is autumn crocus?

Autumn Crocus is rated USDA 4-9 and RHS H7 — Hardy in the severest European continental winters.

Can autumn crocus survive winter outside?

Plant it out within USDA 4-9 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 autumn crocus below its minimum temperature?

It tolerates winter lows to about −20 °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.