Cold hardiness & minimum temperature

Is Caucasian Comfrey (Symphytum caucasicum)cold hardy? Hardiness zone & min temp

Also called Caucasian Comfrey, Blue Comfrey.

More about caucasian comfrey

About Caucasian Comfrey

Symphytum caucasicum · also called Caucasian Comfrey, Blue Comfrey · flowering

Caucasian Comfrey is a vigorous, clump-forming perennial from the Caucasus region bearing bright blue, tubular flowers in spring. It thrives in partial shade and moist soil, spreading readily via rhizomes. An excellent ground cover for shaded banks, it requires minimal care once established but can become invasive in ideal conditions.

Cold limit: USDA 3–9 · RHS H7 (-20 to 25°C)

What caucasian comfrey's hardiness rating actually means

Yes — caucasian comfrey is genuinely cold hardy. Rated RHS H7 and USDA 3–9, 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 3–9 — 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. Caucasian Comfrey is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for caucasian comfrey 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 caucasian comfrey go outside or overwinter — and where?

Plant it out within USDA 3–9 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 caucasian comfrey can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Caucasian Comfrey hardiness — frequently asked questions

Is caucasian comfrey cold hardy?

Yes — caucasian comfrey is genuinely cold hardy. Rated RHS H7 and USDA 3–9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Caucasian Comfrey is hardy across USDA 3–9; 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 caucasian comfrey can survive?

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

What hardiness zone is caucasian comfrey?

Caucasian Comfrey is rated USDA 3–9 and RHS H7 — Hardy in the severest European continental winters.

Can caucasian comfrey survive winter outside?

Plant it out within USDA 3–9 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 caucasian comfrey 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.