Cold hardiness & minimum temperature

Is South African Geranium (Pelargonium sidoides)cold hardy? Hardiness zone & min temp

Also called South African Geranium, Umckaloabo, African Geranium.

More about south african geranium

About South African Geranium

Pelargonium sidoides · also called South African Geranium, Umckaloabo · herb

Pelargonium sidoides is a tuberous-rooted perennial species from the dry grasslands and rocky slopes of South Africa, valued both as an ornamental and as a medicinal herb — its root extract is the basis for Umckaloabo, a widely sold herbal cold and bronchitis remedy. It produces a low, velvety-silver rosette of heart-shaped leaves and abundant small, deep maroon-to-black flowers on upright stems throughout a long season. It needs very free-draining soil and dislikes wet winters, making container culture the safest approach in UK and northern US gardens. Toxic to cats and dogs.

Cold limit: USDA 8-10 (tuberous roots may survive light frost if dry) · RHS H3 (5-28°C)

Watch for — Root and stem rot: The most common cause of death in wet or heavy soils; stems blacken at the base and collapse. Always use very gritty compost, ensure pots drain freely, and keep the plant nearly dry in winter.

What south african geranium's hardiness rating actually means

South African Geranium is half-hardy (RHS H3). 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 H3 means: Half-hardy — comes through mild UK winters outside but is killed by a hard freeze. On the US scale that maps to USDA 8-10 (tuberous roots may survive light frost if dry) — 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 −5 to 1 °C — a light, short frost only. South African Geranium shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for south african geranium as it gets too cold:

Down to roughly about −5 to 1 °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 south african geranium go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-10 (tuberous roots may survive light frost if dry) 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 south african geranium can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H3 figure above.

Frost protection for borderline south african geranium

South African Geranium 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.

South African Geranium hardiness — frequently asked questions

Is south african geranium cold hardy?

South African Geranium is half-hardy (RHS H3). 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 8-10 (tuberous roots may survive light frost if dry) (and sheltered UK gardens) south african geranium can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature south african geranium can survive?

Minimum survivable temperature is roughly about −5 to 1 °C — a light, short frost only. South African Geranium shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is south african geranium?

South African Geranium is rated USDA 8-10 (tuberous roots may survive light frost if dry) and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can south african geranium survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-10 (tuberous roots may survive light frost if dry) 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 south african geranium 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.