Cold hardiness & minimum temperature

Is Wall Rue (Asplenium ruta-muraria)cold hardy? Hardiness zone & min temp

Also called Wall Rue, Wall Rue Spleenwort.

More about wall rue

About Wall Rue

Asplenium ruta-muraria · also called Wall Rue, Wall Rue Spleenwort · flowering

Wall rue (Asplenium ruta-muraria) is a tiny, tufted evergreen spleenwort that colonises mortared walls, limestone rocks and old masonry across Europe. Its small, leathery, ferny fronds are blue-green and parsley-like. A true lime-lover, it is exceptionally drought- and cold-tolerant, thriving in cracks where little else grows, but resents rich soil and disturbance.

Cold limit: USDA 5-8 · RHS H6 (-10-22°C)

What wall rue's hardiness rating actually means

Yes — wall rue is genuinely cold hardy. Rated RHS H6 and USDA 5-8, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H6 means: Hardy throughout the UK and northern Europe. On the US scale that maps to USDA 5-8 — 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 about −20 to −15 °C. Wall Rue is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for wall rue as it gets too cold:

It tolerates winter lows to about −20 to −15 °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 wall rue go outside or overwinter — and where?

Plant it out within USDA 5-8 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 wall rue can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Wall Rue hardiness — frequently asked questions

Is wall rue cold hardy?

Yes — wall rue is genuinely cold hardy. Rated RHS H6 and USDA 5-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Wall Rue is hardy across USDA 5-8; 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 wall rue can survive?

Minimum survivable temperature is roughly about −20 to −15 °C. Wall Rue is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is wall rue?

Wall Rue is rated USDA 5-8 and RHS H6 — Hardy throughout the UK and northern Europe.

Can wall rue survive winter outside?

Plant it out within USDA 5-8 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 wall rue below its minimum temperature?

It tolerates winter lows to about −20 to −15 °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.