Cold hardiness & minimum temperature

Is Fishhook Barrel (Mammillaria spinosissima)cold hardy? Hardiness zone & min temp

Also called Red-Headed Irishman, Spiny Pincushion.

More about fishhook barrel

About Fishhook Barrel

Mammillaria spinosissima · also called Red-Headed Irishman, Spiny Pincushion · houseplant

Mammillaria spinosissima, the 'Red-Headed Irishman', is a cylindrical pincushion cactus densely clothed in stiff spines that range from white through gold to rusty red, often crowning the plant in a fiery cap. In spring it rings its top with deep pink-magenta flowers. Easy and showy, it wants strong sun, very gritty soil, and a cool, dry winter to bloom.

Cold limit: USDA 9-11 (grown indoors or under glass in cooler regions; keep frost-free with a cool dry winter) · RHS H2 (10-30°C)

Watch for — Soft, brown base (rot): Caused by overwatering or a soil mix that holds water. Water only when bone dry, repot into grittier medium, and keep especially dry through winter.

What fishhook barrel's hardiness rating actually means

Fishhook Barrel 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 (grown indoors or under glass in cooler regions; keep frost-free with a cool dry winter) — 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. Fishhook Barrel shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for fishhook barrel 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 fishhook barrel go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (grown indoors or under glass in cooler regions; keep frost-free with a cool dry winter) 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 fishhook barrel 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 fishhook barrel

Fishhook Barrel 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.

Fishhook Barrel hardiness — frequently asked questions

Is fishhook barrel cold hardy?

Fishhook Barrel 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 (grown indoors or under glass in cooler regions; keep frost-free with a cool dry winter) (and sheltered UK gardens) fishhook barrel can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature fishhook barrel can survive?

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

What hardiness zone is fishhook barrel?

Fishhook Barrel is rated USDA 9-11 (grown indoors or under glass in cooler regions; keep frost-free with a cool dry winter) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can fishhook barrel survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (grown indoors or under glass in cooler regions; keep frost-free with a cool dry winter) 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 fishhook barrel 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.