Cold hardiness & minimum temperature

Is Frosty Fern (Selaginella kraussiana 'Frosty')cold hardy? Hardiness zone & min temp

Also called Frosty fern, Frosty spikemoss, Krauss' spikemoss, African clubmoss, Spreading clubmoss.

More about frosty fern

About Frosty Fern

Selaginella kraussiana 'Frosty' · also called Frosty fern, Frosty spikemoss · houseplant

Frosty fern is a mat-forming spikemoss (not a true fern) prized for its lacy green fronds with frosted white tips. It demands constant moisture, high humidity and bright indirect light, making it a classic terrarium plant. The ASPCA lists it as non-toxic to cats, dogs and horses, so it is pet-safe.

Cold limit: USDA 11-12 (frost-tender; grown as a houseplant or under glass elsewhere) (16-24 C)

Watch for — Loss of white frosted tips: The bright tips are strongest in cooler conditions and good light; warm, dim spots fade them. Slightly cooler temps and bright indirect light keep the frosting vivid.

What frosty fern's hardiness rating actually means

Frosty Fern is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Its RHS rating of H1b means: Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season. On the US scale that maps to USDA 11-12 (frost-tender; grown as a houseplant or under glass elsewhere) — 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 10 °C (sustained cold below this is damaging). Frosty Fern has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for frosty fern as it gets too cold:

Below about about 10 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches.
A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover.
Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.

Can frosty fern go outside or overwinter — and where?

It can holiday outdoors in summer once nights are reliably above 10 °C, in shade or dappled light, hardened off gradually.
Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C.
It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.

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 frosty fern can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1b figure above.

Frosty Fern hardiness — frequently asked questions

Is frosty fern cold hardy?

Frosty Fern is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Indoor-only in almost every home. Frosty Fern can only live outside year-round in genuinely frost-free climates (roughly USDA 11-12 (frost-tender; grown as a houseplant or under glass elsewhere)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature frosty fern can survive?

Minimum survivable temperature is roughly about 10 °C (sustained cold below this is damaging). Frosty Fern has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

What hardiness zone is frosty fern?

Frosty Fern is rated USDA 11-12 (frost-tender; grown as a houseplant or under glass elsewhere) and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can frosty fern survive winter outside?

It can holiday outdoors in summer once nights are reliably above 10 °C, in shade or dappled light, hardened off gradually. Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C. It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.

What happens to frosty fern below its minimum temperature?

Below about about 10 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches. A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover. Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.