Cold hardiness & minimum temperature

Is Japanese False Spleenwort (Deparia petersenii)cold hardy? Hardiness zone & min temp

Also called Japanese False Spleenwort, Japanese Lady Fern, Petersen's Lady Fern.

More about japanese false spleenwort

About Japanese False Spleenwort

Deparia petersenii · also called Japanese False Spleenwort, Japanese Lady Fern · houseplant

Deparia petersenii is a deciduous fern native to tropical and subtropical eastern Asia, naturalised and considered invasive in south-eastern USA, Hawaii, and parts of the Pacific. It thrives in consistently moist, humus-rich soils in part to full shade, and spreads slowly via creeping rhizomes to form a graceful ground cover of triangular, blackish-green arching fronds. The single most important care point is to keep the soil reliably moist — drought quickly browns the fronds. Toxicity to cats and dogs has not been assessed by the ASPCA; treat as mildly toxic as a precaution.

Cold limit: USDA 7–10 · RHS H3 (10–28 °C)

What japanese false spleenwort's hardiness rating actually means

Japanese False Spleenwort is half-hardy (RHS H3). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Its RHS rating of H3 means: Half-hardy — comes through mild UK winters outside but is killed by a hard freeze. On the US scale that maps to USDA 7–10 — 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 to 1 °C — a light, short frost only. Japanese False Spleenwort shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for japanese false spleenwort as it gets too cold:

Down to roughly about −5 to 1 °C it copes, especially if dry and sheltered.
A sustained hard frost collapses the top growth; whether it returns depends on whether the roots, crown or tubers froze.
Wet cold is far more lethal than dry cold for this plant — soggy, frozen soil is the usual killer.

Can japanese false spleenwort go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 7–10 or a frost-free UK microclimate.
In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter.
A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

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 japanese false spleenwort can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H3 figure above.

Frost protection for borderline japanese false spleenwort

Japanese False Spleenwort is right on a hardiness edge in many gardens, so if you are pushing it, these measures buy it the margin it needs:

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost.
Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse.
Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones.
Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.

Japanese False Spleenwort hardiness — frequently asked questions

Is japanese false spleenwort cold hardy?

Japanese False Spleenwort is half-hardy (RHS H3). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Borderline outdoors. In its mild end of USDA 7–10 (and sheltered UK gardens) japanese false spleenwort can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature japanese false spleenwort can survive?

Minimum survivable temperature is roughly about −5 to 1 °C — a light, short frost only. Japanese False Spleenwort shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is japanese false spleenwort?

Japanese False Spleenwort is rated USDA 7–10 and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can japanese false spleenwort survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 7–10 or a frost-free UK microclimate. In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter. A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

How do I protect japanese false spleenwort from frost?

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost. Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse. Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones. Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.