Cold hardiness & minimum temperature

Is Ceratopteris cornuta (Ceratopteris cornuta)cold hardy? Hardiness zone & min temp

Also called floating water sprite, horned water fern.

More about ceratopteris cornuta

About Ceratopteris cornuta

Ceratopteris cornuta · also called floating water sprite, horned water fern · tropical

Ceratopteris cornuta, the floating water sprite or horned water fern, is a broad-leaved aquatic fern usually grown drifting at the surface of tropical tanks. Its lighter-green, less finely cut fronds form buoyant rosettes that trail roots into the water, shading fry and absorbing excess nutrients. Like its relatives it multiplies fast via marginal plantlets and helps outcompete algae.

Cold limit: USDA Not applicable (tropical aquarium plant, indoor) · RHS H1b (22-28°C)

What ceratopteris cornuta's hardiness rating actually means

Ceratopteris cornuta 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 Not applicable (tropical aquarium plant, indoor) — 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). Ceratopteris cornuta has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for ceratopteris cornuta 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 ceratopteris cornuta 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 ceratopteris cornuta can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1b figure above.

Ceratopteris cornuta hardiness — frequently asked questions

Is ceratopteris cornuta cold hardy?

Ceratopteris cornuta 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. Ceratopteris cornuta can only live outside year-round in genuinely frost-free climates (roughly USDA Not applicable (tropical aquarium plant, indoor)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature ceratopteris cornuta can survive?

What hardiness zone is ceratopteris cornuta?

Ceratopteris cornuta is rated USDA Not applicable (tropical aquarium plant, indoor) and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can ceratopteris cornuta 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 ceratopteris cornuta 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.