Cold hardiness & minimum temperature

Is Scarlet Ball Cactus (Parodia haselbergii)cold hardy? Hardiness zone & min temp

Also called Scarlet Ball Cactus, White-web Ball Cactus.

More about scarlet ball cactus

About Scarlet Ball Cactus

Parodia haselbergii · also called Scarlet Ball Cactus, White-web Ball Cactus · flowering

The Scarlet Ball Cactus is a flattened South American globe veiled in fine white bristly spines, named for the unusual scarlet-orange flowers it carries in late winter and early spring, earlier than most cacti. The pale spination gives it a frosted look. It needs full sun, very sharp drainage, and a cool dry rest to flower well indoors.

Cold limit: USDA 9-11 (indoor in most US homes); not frost-hardy · RHS H2 (18-27°C in growth; 8-12°C winter rest)

Watch for — Crown and base rot: The flattened, web-spined body holds water easily; overwatering or trapped moisture causes rot. Water at the soil, keep airflow high, and stay nearly dry in winter.

What scarlet ball cactus's hardiness rating actually means

Scarlet Ball 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 in most US homes); not frost-hardy — 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 Ball Cactus shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for scarlet ball 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 scarlet ball 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 in most US homes); not frost-hardy 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 ball 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 scarlet ball cactus

Scarlet Ball 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.

Scarlet Ball Cactus hardiness — frequently asked questions

Is scarlet ball cactus cold hardy?

Scarlet Ball 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 in most US homes); not frost-hardy (and sheltered UK gardens) scarlet ball 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 scarlet ball cactus can survive?

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

What hardiness zone is scarlet ball cactus?

Scarlet Ball Cactus is rated USDA 9-11 (indoor in most US homes); not frost-hardy and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can scarlet ball cactus survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (indoor in most US homes); not frost-hardy 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 ball 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.