Cold hardiness & minimum temperature

Is Mountain Turk's Cap (Melocactus oreas)cold hardy? Hardiness zone & min temp

Also called Mountain Melocactus, Turk's Cap Cactus.

More about mountain turk's cap

About Mountain Turk's Cap

Melocactus oreas · also called Mountain Melocactus, Turk's Cap Cactus · houseplant

Mountain Turk's Cap is a ribbed, globose Brazilian cactus that produces a prominent whitish-grey woolly cephalium crowned with red-orange bristles when it reaches maturity. Unlike many Melocactus, it tolerates slightly cooler conditions, making it one of the more adaptable species in the genus. Small pink flowers appear from the cephalium regularly. Not toxic to pets; spines are the hazard.

Cold limit: USDA 9b-12 (may tolerate brief cool spells better than lowland Melocactus; indoor-only in most climates) · RHS H2 (15-30°C)

Watch for — Cold damage: Although slightly more cool-tolerant than some Melocactus, temperatures consistently below 10°C will damage or kill the plant.

What mountain turk's cap's hardiness rating actually means

Mountain Turk's Cap 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-12 (may tolerate brief cool spells better than lowland Melocactus; indoor-only in most climates) — 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. Mountain Turk's Cap shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for mountain turk's cap 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 mountain turk's cap go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 9b-12 (may tolerate brief cool spells better than lowland Melocactus; indoor-only in most climates) 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 mountain turk's cap 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 mountain turk's cap

Mountain Turk's Cap 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.

Mountain Turk's Cap hardiness — frequently asked questions

Is mountain turk's cap cold hardy?

Mountain Turk's Cap 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-12 (may tolerate brief cool spells better than lowland Melocactus; indoor-only in most climates) (and sheltered UK gardens) mountain turk's cap can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature mountain turk's cap can survive?

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

What hardiness zone is mountain turk's cap?

Mountain Turk's Cap is rated USDA 9b-12 (may tolerate brief cool spells better than lowland Melocactus; indoor-only in most climates) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can mountain turk's cap survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9b-12 (may tolerate brief cool spells better than lowland Melocactus; indoor-only in most climates) 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 mountain turk's cap 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.