Cold hardiness & minimum temperature

Is Woodsia ilvensis (Woodsia ilvensis)cold hardy? Hardiness zone & min temp

Also called Rusty Woodsia, Fragrant Woodsia.

More about woodsia ilvensis

About Woodsia ilvensis

Woodsia ilvensis · also called Rusty Woodsia, Fragrant Woodsia · flowering

Woodsia ilvensis, the rusty woodsia, is a small, hardy alpine fern of rocky outcrops across the cool northern hemisphere. Its narrow, twice-cut fronds carry rusty-brown scales and hairs beneath, giving the plant its name. A tough crevice dweller adapted to lean, gritty ground and cold exposure, it is a connoisseur's choice for alpine troughs and rock gardens.

Cold limit: USDA 2-7 (extremely cold-hardy, deciduous) · RHS H7 (5-21°C)

Watch for — Crown rot from overwatering: Wet, poorly drained soil is fatal to this alpine. Use very sharp drainage and keep water off the crown, especially in winter.

What woodsia ilvensis's hardiness rating actually means

Yes — woodsia ilvensis is genuinely cold hardy. Rated RHS H7 and USDA 2-7 (extremely cold-hardy, deciduous), 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 2-7 (extremely cold-hardy, deciduous) — 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. Woodsia ilvensis is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for woodsia ilvensis 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 woodsia ilvensis go outside or overwinter — and where?

Plant it out within USDA 2-7 (extremely cold-hardy, deciduous) 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 woodsia ilvensis can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Woodsia ilvensis hardiness — frequently asked questions

Is woodsia ilvensis cold hardy?

Yes — woodsia ilvensis is genuinely cold hardy. Rated RHS H7 and USDA 2-7 (extremely cold-hardy, deciduous), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Woodsia ilvensis is hardy across USDA 2-7 (extremely cold-hardy, deciduous); 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 woodsia ilvensis can survive?

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

What hardiness zone is woodsia ilvensis?

Woodsia ilvensis is rated USDA 2-7 (extremely cold-hardy, deciduous) and RHS H7 — Hardy in the severest European continental winters.

Can woodsia ilvensis survive winter outside?

Plant it out within USDA 2-7 (extremely cold-hardy, deciduous) 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 woodsia ilvensis 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.