Cold hardiness & minimum temperature

Is Dunn's cape primrose (Streptocarpus dunnii)cold hardy? Hardiness zone & min temp

Also called Dunn's cape primrose, Red cape primrose.

More about dunn's cape primrose

About Dunn's cape primrose

Streptocarpus dunnii · also called Dunn's cape primrose, Red cape primrose · houseplant

A dramatic monocarpic unifoliate species bearing a single large, continuously-growing hairy leaf (up to 600 mm long) and vivid orange-red trumpet flowers produced densely at the leaf base. It blooms once and then dies, making seed the only propagation route. A specialist collector's plant requiring careful moisture management.

Cold limit: USDA 10–11 · RHS H1c (15–22°C)

What dunn's cape primrose's hardiness rating actually means

Dunn's 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 10–11 — 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). Dunn's cape primrose has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for dunn's 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 dunn's 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 dunn's 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.

Dunn's cape primrose hardiness — frequently asked questions

Is dunn's cape primrose cold hardy?

Dunn's 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. Dunn's cape primrose can only live outside year-round in genuinely frost-free climates (roughly USDA 10–11); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature dunn's cape primrose can survive?

Minimum survivable temperature is roughly about 5 °C (and never frost). Dunn's cape primrose has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

What hardiness zone is dunn's cape primrose?

Dunn's cape primrose is rated USDA 10–11 and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can dunn's 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 dunn's 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.