Cold hardiness & minimum temperature

Is Johannes Cape Primrose (Streptocarpus johannis)cold hardy? Hardiness zone & min temp

Also called Johannes Cape Primrose, Cape Primrose.

More about johannes cape primrose

About Johannes Cape Primrose

Streptocarpus johannis · also called Johannes Cape Primrose, Cape Primrose · flowering

Streptocarpus johannis is a compact rosulate species found in the Eastern Cape and KwaZulu-Natal provinces of South Africa, typically growing on damp, shaded cliff faces and forest floors. It produces small, pale lavender to white flowers with a distinctive yellow or cream guide-stripe in the throat. Its compact size makes it suitable for windowsill culture, but it demands cool, humid conditions and must never be allowed to dry out completely, as its small root system recovers poorly from severe drought. It is non-toxic to cats and dogs per the ASPCA.

Cold limit: USDA 10-12 (indoor in most climates) · RHS H1b (12-22°C)

What johannes cape primrose's hardiness rating actually means

Johannes 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 10-12 (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 10 °C (sustained cold below this is damaging). Johannes Cape Primrose has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for johannes 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 johannes 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 johannes 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.

Johannes Cape Primrose hardiness — frequently asked questions

Is johannes cape primrose cold hardy?

Johannes 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. Johannes 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 johannes cape primrose can survive?

What hardiness zone is johannes cape primrose?

Johannes Cape Primrose is rated USDA 10-12 (indoor in most climates) and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can johannes 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 johannes 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.