Cold hardiness & minimum temperature

Is Almost-round Cape Primrose (Streptocarpus suborbicularis)cold hardy? Hardiness zone & min temp

Also called Almost-round Cape Primrose, Cape Primrose.

More about almost-round cape primrose

About Almost-round Cape Primrose

Streptocarpus suborbicularis · also called Almost-round Cape Primrose, Cape Primrose · houseplant

Streptocarpus suborbicularis is a species native to South Africa, its name referring to its nearly circular (suborbicular) leaf shape, which distinguishes it within the genus. It belongs to the unifoliate or rosulate section of Streptocarpus, growing in shaded, rocky habitats in the eastern regions of South Africa. Like other Cape Primroses, it produces tubular flowers from the leaf midrib and requires bright indirect light, moderate moisture, and well-draining compost. The most important care principle is to water carefully — always from the base — to prevent crown rot. According to the ASPCA, the Streptocarpus genus is non-toxic to cats, dogs, and horses.

Cold limit: USDA 10-12 (indoor in most climates) · RHS H1c (15–24°C)

What almost-round cape primrose's hardiness rating actually means

Almost-round Cape Primrose is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Its RHS rating of H1c means: Warm-temperate — can summer outdoors but must come in well before the first frost. On the US scale that maps to USDA 10-12 (indoor 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 5 °C (and never frost). Almost-round Cape Primrose has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for almost-round cape primrose as it gets too cold:

Below about about 5 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches.
A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover.
Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.

Can almost-round cape primrose go outside or overwinter — and where?

It can holiday outdoors in summer once nights are reliably above 5 °C, in shade or dappled light, hardened off gradually.
Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C.
It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.

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 almost-round cape primrose can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1c figure above.

Almost-round Cape Primrose hardiness — frequently asked questions

Is almost-round cape primrose cold hardy?

Almost-round Cape Primrose is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Indoor-only in almost every home. Almost-round Cape Primrose can only live outside year-round in genuinely frost-free climates (roughly USDA 10-12 (indoor in most climates)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature almost-round cape primrose can survive?

Minimum survivable temperature is roughly about 5 °C (and never frost). Almost-round Cape Primrose has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

What hardiness zone is almost-round cape primrose?

Almost-round Cape Primrose is rated USDA 10-12 (indoor in most climates) and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can almost-round cape primrose survive winter outside?

It can holiday outdoors in summer once nights are reliably above 5 °C, in shade or dappled light, hardened off gradually. Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C. It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.

What happens to almost-round cape primrose below its minimum temperature?

Below about about 5 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches. A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover. Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.