Cold hardiness & minimum temperature

Is Goat's Horn Cactus (Astrophytum capricorne)cold hardy? Hardiness zone & min temp

Also called Goat Horn Cactus.

More about goat's horn cactus

About Goat's Horn Cactus

Astrophytum capricorne · also called Goat Horn Cactus · flowering

Astrophytum capricorne is a slow-growing globular cactus prized for its long, twisting papery spines that curl like a goat's horns over a green body flecked with white scales. Mature plants produce large yellow blooms with red throats in summer. Give it blazing sun, gritty soil, and a bone-dry winter rest to thrive.

Cold limit: USDA 9-11 (indoor or under cover in most US homes) · RHS H2 (18-30°C)

Watch for — Root rot: The single most common killer. Caused by overwatering, dense soil, or winter watering. Use gritty mix and let soil dry fully between drinks.

What goat's horn cactus's hardiness rating actually means

Goat's Horn 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 9-11 (indoor or under cover 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. Goat's Horn Cactus shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for goat's horn 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 goat's horn cactus 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 under cover 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 goat's horn 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 goat's horn cactus

Goat's Horn 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.

Goat's Horn Cactus hardiness — frequently asked questions

Is goat's horn cactus cold hardy?

Goat's Horn 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 9-11 (indoor or under cover in most US homes) (and sheltered UK gardens) goat's horn 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 goat's horn cactus can survive?

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

What hardiness zone is goat's horn cactus?

Goat's Horn Cactus is rated USDA 9-11 (indoor or under cover in most US homes) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can goat's horn cactus survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (indoor or under cover 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 goat's horn 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.