Cold hardiness & minimum temperature

Is Steinmann's Rebutia (Rebutia steinmannii)cold hardy? Hardiness zone & min temp

Also called Steinmann's Rebutia, Purple Crown Cactus.

More about steinmann's rebutia

About Steinmann's Rebutia

Rebutia steinmannii · also called Steinmann's Rebutia, Purple Crown Cactus · houseplant

A dwarf, clump-forming crown cactus from Bolivia with small globose stems and short, neat spines. Produces a profusion of vivid purple to magenta-pink funnel-shaped flowers in spring. Mountain-adapted and more cold-tolerant than many cacti, it benefits from a cool, dry winter rest to trigger flowering. Compact size makes it ideal for windowsill collections.

Cold limit: USDA 9a–11b · RHS H2 (2–30°C)

Watch for — Root rot: Overwatering or poor drainage causes the stem base to collapse. Allow the soil to dry completely between waterings and ensure the pot drains freely. In winter, keep the mix almost completely dry.

What steinmann's rebutia's hardiness rating actually means

Steinmann's Rebutia 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 9a–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. Steinmann's Rebutia shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for steinmann's rebutia 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 steinmann's rebutia go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 9a–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 steinmann's rebutia 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 steinmann's rebutia

Steinmann's Rebutia 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.

Steinmann's Rebutia hardiness — frequently asked questions

Is steinmann's rebutia cold hardy?

Steinmann's Rebutia 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 9a–11b (and sheltered UK gardens) steinmann's rebutia can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature steinmann's rebutia can survive?

Minimum survivable temperature is roughly about 1 to 5 °C — tolerates cold but no real frost. Steinmann's Rebutia shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is steinmann's rebutia?

Steinmann's Rebutia is rated USDA 9a–11b and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can steinmann's rebutia survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9a–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 steinmann's rebutia 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.