Cold hardiness & minimum temperature

Is Cotyledon Orbiculata (Cotyledon orbiculata)cold hardy? Hardiness zone & min temp

Also called pig's ear, round-leafed navel wort, silver crown.

More about cotyledon orbiculata

About Cotyledon Orbiculata

Cotyledon orbiculata · also called pig's ear, round-leafed navel wort · houseplant

Cotyledon orbiculata, or pig's ear, is a robust South African shrub with thick, paddle-shaped grey-green leaves dusted in chalky white and often edged in red. It forms a stout, woody-stemmed bush topped by clusters of orange, bell-shaped flowers. Tough and drought-hardy, it needs full light and sharp drainage. All parts are toxic to pets, containing cardiac glycosides.

Cold limit: USDA 9-11 (indoor or container in colder US zones) · RHS H3 (10-27°C)

What cotyledon orbiculata's hardiness rating actually means

Cotyledon Orbiculata 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 9-11 (indoor or container in colder US zones) — 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. Cotyledon Orbiculata shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for cotyledon orbiculata 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 cotyledon orbiculata go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (indoor or container in colder US zones) 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 cotyledon orbiculata 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 cotyledon orbiculata

Cotyledon Orbiculata 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.

Cotyledon Orbiculata hardiness — frequently asked questions

Is cotyledon orbiculata cold hardy?

Cotyledon Orbiculata 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 9-11 (indoor or container in colder US zones) (and sheltered UK gardens) cotyledon orbiculata can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature cotyledon orbiculata can survive?

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

What hardiness zone is cotyledon orbiculata?

Cotyledon Orbiculata is rated USDA 9-11 (indoor or container in colder US zones) and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can cotyledon orbiculata survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (indoor or container in colder US zones) 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 cotyledon orbiculata 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.