Cold hardiness & minimum temperature

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

Also called Blunt-lobed Woodsia, Common Woodsia.

More about woodsia obtusa

About Woodsia obtusa

Woodsia obtusa · also called Blunt-lobed Woodsia, Common Woodsia · flowering

Woodsia obtusa, the blunt-lobed woodsia, is a small, tufted North American fern of rocky slopes, ledges and dry woodlands. Its lacy, blue-green, twice-cut fronds form neat clumps that tolerate more sun and drier, rockier ground than most ferns. Hardy and adaptable, it is a charming choice for rock gardens, crevices and shaded stone walls.

Cold limit: USDA 4-8 (deciduous, very cold-hardy) · RHS H6 (10-24°C)

What woodsia obtusa's hardiness rating actually means

Yes — woodsia obtusa is genuinely cold hardy. Rated RHS H6 and USDA 4-8 (deciduous, very cold-hardy), 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 4-8 (deciduous, very cold-hardy) — 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. Woodsia obtusa is built for winter — once established it takes hard frost and snow in its stride.

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

Plant it out within USDA 4-8 (deciduous, very cold-hardy) 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 obtusa can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Woodsia obtusa hardiness — frequently asked questions

Is woodsia obtusa cold hardy?

Yes — woodsia obtusa is genuinely cold hardy. Rated RHS H6 and USDA 4-8 (deciduous, very cold-hardy), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Woodsia obtusa is hardy across USDA 4-8 (deciduous, very cold-hardy); 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 obtusa can survive?

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

What hardiness zone is woodsia obtusa?

Woodsia obtusa is rated USDA 4-8 (deciduous, very cold-hardy) and RHS H6 — Hardy throughout the UK and northern Europe.

Can woodsia obtusa survive winter outside?

Plant it out within USDA 4-8 (deciduous, very cold-hardy) 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 obtusa 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.