Cold hardiness & minimum temperature

Is Hollow-Rooted Fumewort (Corydalis cava)cold hardy? Hardiness zone & min temp

Also called Hollow-rooted fumewort, Hollow fumewort, Bird-in-a-bush.

More about hollow-rooted fumewort

About Hollow-Rooted Fumewort

Corydalis cava · also called Hollow-rooted fumewort, Hollow fumewort · flowering

Corydalis cava is a spring-ephemeral tuberous perennial native across a broad swathe of central and southern Europe, from the Pyrenees to Ukraine, colonising shaded woodland floors, hedgebanks, and rocky slopes. In late winter and early spring it produces elegant racemes of white, pale lilac, or purple spurred flowers before the divided, glaucous foliage yellows and vanishes by early summer. Its common name refers to the distinctive hollow centre of the mature tuber, in contrast to the solid tuber of C. bulbosa. Plant it under deciduous trees in humus-rich soil and let it self-seed to naturalise. All parts are toxic to cats and dogs.

Cold limit: USDA 4-8 · RHS H7 (-20 to 18 °C)

What hollow-rooted fumewort's hardiness rating actually means

Yes — hollow-rooted fumewort is genuinely cold hardy. Rated RHS H7 and USDA 4-8, 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 4-8 — 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. Hollow-Rooted Fumewort is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for hollow-rooted fumewort 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 hollow-rooted fumewort go outside or overwinter — and where?

Plant it out within USDA 4-8 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 hollow-rooted fumewort can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Hollow-Rooted Fumewort hardiness — frequently asked questions

Is hollow-rooted fumewort cold hardy?

Yes — hollow-rooted fumewort is genuinely cold hardy. Rated RHS H7 and USDA 4-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Hollow-Rooted Fumewort is hardy across USDA 4-8; 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 hollow-rooted fumewort can survive?

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

What hardiness zone is hollow-rooted fumewort?

Hollow-Rooted Fumewort is rated USDA 4-8 and RHS H7 — Hardy in the severest European continental winters.

Can hollow-rooted fumewort survive winter outside?

Plant it out within USDA 4-8 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 hollow-rooted fumewort 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.