Cold hardiness & minimum temperature

Is Limestone Oak Fern (Gymnocarpium robertianum)cold hardy? Hardiness zone & min temp

Also called Limestone Oak Fern, Scented Oak Fern.

More about limestone oak fern

About Limestone Oak Fern

Gymnocarpium robertianum · also called Limestone Oak Fern, Scented Oak Fern · flowering

Limestone oak fern (Gymnocarpium robertianum) is a deciduous fern of limestone screes, pavements and old walls, the lime-loving counterpart to common oak fern. Its slightly greyer-green, triangular fronds are faintly aromatic when crushed and held on slender stalks. Spreading gently by rhizomes, it thrives in cool, alkaline, sharply drained shade and dies back in winter.

Cold limit: USDA 4-7 · RHS H6 (-10-22°C)

What limestone oak fern's hardiness rating actually means

Yes — limestone oak fern is genuinely cold hardy. Rated RHS H6 and USDA 4-7, 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 4-7 — 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. Limestone Oak Fern is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for limestone oak fern 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 limestone oak fern go outside or overwinter — and where?

Plant it out within USDA 4-7 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 limestone oak fern can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Limestone Oak Fern hardiness — frequently asked questions

Is limestone oak fern cold hardy?

Yes — limestone oak fern is genuinely cold hardy. Rated RHS H6 and USDA 4-7, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Limestone Oak Fern is hardy across USDA 4-7; 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 limestone oak fern can survive?

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

What hardiness zone is limestone oak fern?

Limestone Oak Fern is rated USDA 4-7 and RHS H6 — Hardy throughout the UK and northern Europe.

Can limestone oak fern survive winter outside?

Plant it out within USDA 4-7 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 limestone oak fern 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.