Cold hardiness & minimum temperature

Is Cinnamon Fern (Osmundastrum cinnamomeum)cold hardy? Hardiness zone & min temp

Also called Cinnamon fern.

More about cinnamon fern

About Cinnamon Fern

Osmundastrum cinnamomeum · also called Cinnamon fern · houseplant

The cinnamon fern is a large, deciduous native fern named for the cinnamon-coloured fertile fronds that rise like spires from the centre of a vase of tall green sterile fronds. A wetland and streamside plant, it demands cool, moist to wet, acidic ground and shade. Bold and architectural, it suits damp woodland gardens and bog margins.

Cold limit: USDA 3-9 (outdoors) · RHS H7 (5-24°C)

What cinnamon fern's hardiness rating actually means

Yes — cinnamon fern is genuinely cold hardy. Rated RHS H7 and USDA 3-9 (outdoors), 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 (outdoors) — 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. Cinnamon Fern is built for winter — once established it takes hard frost and snow in its stride.

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

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

Cinnamon Fern hardiness — frequently asked questions

Is cinnamon fern cold hardy?

Yes — cinnamon fern is genuinely cold hardy. Rated RHS H7 and USDA 3-9 (outdoors), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Cinnamon Fern is hardy across USDA 3-9 (outdoors); 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 cinnamon fern can survive?

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

What hardiness zone is cinnamon fern?

Cinnamon Fern is rated USDA 3-9 (outdoors) and RHS H7 — Hardy in the severest European continental winters.

Can cinnamon fern survive winter outside?

Plant it out within USDA 3-9 (outdoors) 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 cinnamon fern 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.