Cold hardiness & minimum temperature

Is Cape Primrose (Streptocarpus 'Crystal Ice')cold hardy? Hardiness zone & min temp

Also called Streptocarpus, Cape Primrose.

More about cape primrose

About Cape Primrose

Streptocarpus 'Crystal Ice' · also called Streptocarpus, Cape Primrose · flowering

Cape Primrose 'Crystal Ice' is a Streptocarpus cultivar grown for long flushes of white flowers veined with violet-blue, held above strappy, soft green leaves. A gesneriad relative of the African violet, it flowers for months on a cool, bright windowsill, prefers to dry slightly between waterings and dislikes hot, soggy conditions. It is pet-safe.

Cold limit: USDA 10-11 (grown as an indoor plant) · RHS H1b (15-24°C)

What cape primrose's hardiness rating actually means

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 H1b means: Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season. On the US scale that maps to USDA 10-11 (grown as an indoor plant) — 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 10 °C (sustained cold below this is damaging). Cape Primrose has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for cape primrose as it gets too cold:

Below about about 10 °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 cape primrose go outside or overwinter — and where?

It can holiday outdoors in summer once nights are reliably above 10 °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 cape primrose can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1b figure above.

Cape Primrose hardiness — frequently asked questions

Is cape primrose cold hardy?

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. Cape Primrose can only live outside year-round in genuinely frost-free climates (roughly USDA 10-11 (grown as an indoor plant)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature cape primrose can survive?

What hardiness zone is cape primrose?

Cape Primrose is rated USDA 10-11 (grown as an indoor plant) and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can cape primrose survive winter outside?

It can holiday outdoors in summer once nights are reliably above 10 °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 cape primrose below its minimum temperature?

Below about about 10 °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.