Cold hardiness & minimum temperature

Is Fishbone Fern (Nephrolepis cordifolia 'Plumosa')cold hardy? Hardiness zone & min temp

Also called Fishbone Fern, Plumosa Fern.

More about fishbone fern

About Fishbone Fern

Nephrolepis cordifolia 'Plumosa' · also called Fishbone Fern, Plumosa Fern · houseplant

Fishbone fern is a tough, upright relative of the Boston fern with narrow, ladder-like fronds whose neat paired leaflets resemble a fishbone. The 'Plumosa' form adds frillier, feathered pinnae. It is one of the most forgiving ferns indoors, tolerating ordinary rooms, and spreads by wiry runners and small tubers, making it easy to share by division.

Cold limit: USDA 9-11 (a houseplant in cooler zones; invasive outdoors in warm regions) · RHS H1c (16-24°C)

What fishbone fern's hardiness rating actually means

Fishbone 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 H1c means: Warm-temperate — can summer outdoors but must come in well before the first frost. On the US scale that maps to USDA 9-11 (a houseplant in cooler zones; invasive outdoors in warm regions) — 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 5 °C (and never frost). Fishbone Fern has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for fishbone fern as it gets too cold:

Below about about 5 °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 fishbone fern go outside or overwinter — and where?

It can holiday outdoors in summer once nights are reliably above 5 °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 fishbone fern can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1c figure above.

Fishbone Fern hardiness — frequently asked questions

Is fishbone fern cold hardy?

Fishbone 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. Fishbone Fern can only live outside year-round in genuinely frost-free climates (roughly USDA 9-11 (a houseplant in cooler zones; invasive outdoors in warm regions)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature fishbone fern can survive?

Minimum survivable temperature is roughly about 5 °C (and never frost). Fishbone Fern has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

What hardiness zone is fishbone fern?

Fishbone Fern is rated USDA 9-11 (a houseplant in cooler zones; invasive outdoors in warm regions) and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can fishbone fern survive winter outside?

It can holiday outdoors in summer once nights are reliably above 5 °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 fishbone fern below its minimum temperature?

Below about about 5 °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.