Cold hardiness & minimum temperature

Is White-haired Crown Cactus (Rebutia muscula)cold hardy? Hardiness zone & min temp

Also called White-haired Crown Cactus, Orange Snowball Cactus, Little Mouse Cactus.

More about white-haired crown cactus

About White-haired Crown Cactus

Rebutia muscula · also called White-haired Crown Cactus, Orange Snowball Cactus · houseplant

A small Bolivian mountain cactus densely clothed in soft, bristly white to yellowish spines that completely obscure the dark green body, giving it a distinctive fuzzy appearance. Produces vivid orange-red, funnel-shaped flowers in early to mid-summer. Compact and free-flowering, it is an excellent choice for bright windowsills. RHS Award of Garden Merit holder.

Cold limit: USDA 9b–11b · RHS H2 (1–30°C)

Watch for — No flowering: Cool, dry winter dormancy at 5–10°C (41–50°F) is essential to trigger spring/summer blooms. Plants kept too warm and damp in winter rarely flower. Ensure adequate direct sun throughout the growing season.

What white-haired crown cactus's hardiness rating actually means

White-haired Crown Cactus is half-hardy (RHS H2). 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 H2 means: Tender — survives a frost-free greenhouse or a very mild, sheltered spot. On the US scale that maps to USDA 9b–11b — 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 1 to 5 °C — tolerates cold but no real frost. White-haired Crown Cactus shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for white-haired crown cactus as it gets too cold:

Down to roughly about 1 to 5 °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 white-haired crown cactus go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 9b–11b 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 white-haired crown cactus can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H2 figure above.

Frost protection for borderline white-haired crown cactus

White-haired Crown Cactus 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.

White-haired Crown Cactus hardiness — frequently asked questions

Is white-haired crown cactus cold hardy?

White-haired Crown Cactus is half-hardy (RHS H2). 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 9b–11b (and sheltered UK gardens) white-haired crown cactus can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature white-haired crown cactus can survive?

Minimum survivable temperature is roughly about 1 to 5 °C — tolerates cold but no real frost. White-haired Crown Cactus shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is white-haired crown cactus?

White-haired Crown Cactus is rated USDA 9b–11b and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can white-haired crown cactus survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9b–11b 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 white-haired crown cactus 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.