Cold hardiness & minimum temperature

Is Tuberous Cranesbill (Geranium tuberosum)cold hardy? Hardiness zone & min temp

Also called Tuberous Cranesbill, Tuberous-Rooted Cranesbill.

More about tuberous cranesbill

About Tuberous Cranesbill

Geranium tuberosum · also called Tuberous Cranesbill, Tuberous-Rooted Cranesbill · flowering

Geranium tuberosum is a spring-flowering cranesbill native to the Mediterranean basin east to Iran, growing from small underground tubers. It behaves like a spring ephemeral: finely divided foliage emerges in late winter, lilac-pink veined flowers appear in spring, and the whole plant retreats into summer dormancy by early summer. The most important care fact is to provide a sunny, sharply drained position and allow the soil to dry out completely in summer — wet summer soils rot the tubers. ASPCA's toxic 'Geranium' entry refers to Pelargonium; true Geranium cranesbills are not individually listed as toxic, but ASPCA does not confirm them as non-toxic either, so treat with caution around pets.

Cold limit: USDA 6-9 · RHS H5 (-15°C to 25°C (active growth 5–20°C))

Watch for — Tuber rot in summer: Tubers left in waterlogged or moist soil during summer dormancy quickly rot; ensure excellent drainage and a dry position, or lift tubers and store dry in a cool frost-free place.

What tuberous cranesbill's hardiness rating actually means

Yes — tuberous cranesbill is genuinely cold hardy. Rated RHS H5 and USDA 6-9, 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 — 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. Tuberous Cranesbill is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for tuberous cranesbill 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 tuberous cranesbill go outside or overwinter — and where?

Plant it out within USDA 6-9 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 tuberous cranesbill can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Tuberous Cranesbill hardiness — frequently asked questions

Is tuberous cranesbill cold hardy?

Yes — tuberous cranesbill is genuinely cold hardy. Rated RHS H5 and USDA 6-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Tuberous Cranesbill is hardy across USDA 6-9; 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 tuberous cranesbill can survive?

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

What hardiness zone is tuberous cranesbill?

Tuberous Cranesbill is rated USDA 6-9 and RHS H5 — Hardy in most of the UK and in cold winters.

Can tuberous cranesbill survive winter outside?

Plant it out within USDA 6-9 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 tuberous cranesbill 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.