Cold hardiness & minimum temperature

Is Russian Comfrey (Symphytum x uplandicum)cold hardy? Hardiness zone & min temp

Also called Russian comfrey, hybrid comfrey, blue comfrey.

More about russian comfrey

About Russian Comfrey

Symphytum x uplandicum · also called Russian comfrey, hybrid comfrey · herb

Russian comfrey is a vigorous hybrid of common and rough comfrey, grown as a high-yield permaculture fertiliser crop. It produces masses of large leaves rich in potassium for liquid feed and mulch, plus blue-purple bee flowers. Deep-rooted and tough, it tolerates most soils and gives several cuts a year, though its roots make it hard to eradicate.

Cold limit: USDA 3-9 (fully hardy perennial) · RHS H7 (-1 to 30°C)

What russian comfrey's hardiness rating actually means

Yes — russian comfrey is genuinely cold hardy. Rated RHS H7 and USDA 3-9 (fully 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 3-9 (fully 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. Russian Comfrey is built for winter — once established it takes hard frost and snow in its stride.

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

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

Russian Comfrey hardiness — frequently asked questions

Is russian comfrey cold hardy?

Yes — russian comfrey is genuinely cold hardy. Rated RHS H7 and USDA 3-9 (fully hardy perennial), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Russian Comfrey is hardy across USDA 3-9 (fully 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 russian comfrey can survive?

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

What hardiness zone is russian comfrey?

Russian Comfrey is rated USDA 3-9 (fully hardy perennial) and RHS H7 — Hardy in the severest European continental winters.

Can russian comfrey survive winter outside?

Plant it out within USDA 3-9 (fully 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 russian 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.