Cold hardiness & minimum temperature

Is Crispum Hart's Tongue Fern (Asplenium scolopendrium 'Crispum')cold hardy? Hardiness zone & min temp

Also called Crispum Hart's Tongue Fern, Ruffled Hart's Tongue.

More about crispum hart's tongue fern

About Crispum Hart's Tongue Fern

Asplenium scolopendrium 'Crispum' · also called Crispum Hart's Tongue Fern, Ruffled Hart's Tongue · houseplant

Crispum hart's tongue fern is an ornamental form of the native hart's tongue, prized for its broad, undivided, strap-shaped fronds with heavily frilled and crisped wavy margins. An evergreen woodland fern, it forms glossy shuttlecock rosettes and thrives in cool shade on moist, alkaline soil, reaching around 30-45 cm tall as a hardy, easy plant.

Cold limit: USDA 5-9 (fully hardy outdoors; prefers cool conditions indoors) · RHS H6 (5-21°C)

Watch for — Browning frond margins: Caused by dry air or letting soil dry out. Keep soil evenly moist and raise humidity, particularly indoors in winter.

What crispum hart's tongue fern's hardiness rating actually means

Yes — crispum hart's tongue fern is genuinely cold hardy. Rated RHS H6 and USDA 5-9 (fully hardy outdoors; prefers cool conditions indoors), 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 5-9 (fully hardy outdoors; prefers cool conditions indoors) — 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. Crispum Hart's Tongue Fern is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for crispum hart's tongue 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 crispum hart's tongue fern go outside or overwinter — and where?

Plant it out within USDA 5-9 (fully hardy outdoors; prefers cool conditions indoors) 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 crispum hart's tongue fern can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Crispum Hart's Tongue Fern hardiness — frequently asked questions

Is crispum hart's tongue fern cold hardy?

Yes — crispum hart's tongue fern is genuinely cold hardy. Rated RHS H6 and USDA 5-9 (fully hardy outdoors; prefers cool conditions indoors), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Crispum Hart's Tongue Fern is hardy across USDA 5-9 (fully hardy outdoors; prefers cool conditions indoors); 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 crispum hart's tongue fern can survive?

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

What hardiness zone is crispum hart's tongue fern?

Crispum Hart's Tongue Fern is rated USDA 5-9 (fully hardy outdoors; prefers cool conditions indoors) and RHS H6 — Hardy throughout the UK and northern Europe.

Can crispum hart's tongue fern survive winter outside?

Plant it out within USDA 5-9 (fully hardy outdoors; prefers cool conditions indoors) 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 crispum hart's tongue 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.