Cold hardiness & minimum temperature

Is Geranium phaeum (Geranium phaeum)cold hardy? Hardiness zone & min temp

Also called Dusky cranesbill, Mourning widow geranium, Black widow geranium.

More about geranium phaeum

About Geranium phaeum

Geranium phaeum · also called Dusky cranesbill, Mourning widow geranium · flowering

Geranium phaeum, the dusky cranesbill or mourning widow, is a clump-forming woodland perennial grown for its small, reflexed flowers in deep maroon-purple to near-black, held on slender stems above soft, often blotched leaves in late spring and early summer. One of the best hardy geraniums for shade and dry shade, it self-seeds gently and naturalises beautifully beneath trees and shrubs.

Cold limit: USDA 4-8 (outdoor hardy perennial) · RHS H7 (-25 to 25°C)

What geranium phaeum's hardiness rating actually means

Yes — geranium phaeum is genuinely cold hardy. Rated RHS H7 and USDA 4-8 (outdoor hardy perennial), 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 (outdoor hardy perennial) — 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. Geranium phaeum is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for geranium phaeum 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 geranium phaeum go outside or overwinter — and where?

Plant it out within USDA 4-8 (outdoor hardy perennial) 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 geranium phaeum can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Geranium phaeum hardiness — frequently asked questions

Is geranium phaeum cold hardy?

Yes — geranium phaeum is genuinely cold hardy. Rated RHS H7 and USDA 4-8 (outdoor hardy perennial), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Geranium phaeum is hardy across USDA 4-8 (outdoor hardy perennial); 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 geranium phaeum can survive?

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

What hardiness zone is geranium phaeum?

Geranium phaeum is rated USDA 4-8 (outdoor hardy perennial) and RHS H7 — Hardy in the severest European continental winters.

Can geranium phaeum survive winter outside?

Plant it out within USDA 4-8 (outdoor hardy perennial) 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 geranium phaeum 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.