Cold hardiness & minimum temperature

Is Scarlet Cleistocactus (Cleistocactus winteri)cold hardy? Hardiness zone & min temp

Also called Golden Rat Tail Cactus, Orange Cleistocactus.

More about scarlet cleistocactus

About Scarlet Cleistocactus

Cleistocactus winteri · also called Golden Rat Tail Cactus, Orange Cleistocactus · houseplant

Cleistocactus winteri is a Bolivian cactus with soft golden-spined, pendent to semi-trailing stems, perfect for a hanging pot or raised ledge. Established plants produce vivid orange to salmon tubular flowers along the stems in spring and summer. Easy, fast-growing, and showy, it combines a graceful trailing habit with bright bloom for a sunny indoor spot.

Cold limit: USDA 9-11 (frost-tender; indoor in most US homes) · RHS H2 (10-30°C)

Watch for — Few or no flowers: Insufficient light or no winter rest suppresses blooming. Give strong sun and a cooler, drier winter.

What scarlet cleistocactus's hardiness rating actually means

Scarlet Cleistocactus 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 9-11 (frost-tender; indoor in most US homes) — 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. Scarlet Cleistocactus shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for scarlet cleistocactus 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 scarlet cleistocactus go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (frost-tender; indoor in most US homes) 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 scarlet cleistocactus 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 scarlet cleistocactus

Scarlet Cleistocactus 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.

Scarlet Cleistocactus hardiness — frequently asked questions

Is scarlet cleistocactus cold hardy?

Scarlet Cleistocactus 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 9-11 (frost-tender; indoor in most US homes) (and sheltered UK gardens) scarlet cleistocactus can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature scarlet cleistocactus can survive?

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

What hardiness zone is scarlet cleistocactus?

Scarlet Cleistocactus is rated USDA 9-11 (frost-tender; indoor in most US homes) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can scarlet cleistocactus survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (frost-tender; indoor in most US homes) 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 scarlet cleistocactus 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.