Cold hardiness & minimum temperature

Is Grand Cape Primrose (Streptocarpus grandis)cold hardy? Hardiness zone & min temp

Also called Grand Cape Primrose, Large-leaved Cape Primrose.

More about grand cape primrose

About Grand Cape Primrose

Streptocarpus grandis · also called Grand Cape Primrose, Large-leaved Cape Primrose · flowering

Streptocarpus grandis is a unifoliate species from KwaZulu-Natal, South Africa, notable for producing a single enormous leaf that can exceed 40 cm in length — among the largest of any Streptocarpus species. The plant flowers from the leaf midrib on erect scapes bearing pale lilac to white blooms with a yellow throat. Because it has only one leaf and is monocarpic in its natural growth phase, protecting that leaf from mechanical damage and rot is the single most critical care task. It is listed as non-toxic to cats and dogs by the ASPCA.

Cold limit: USDA 10-12 (indoor in most climates) · RHS H1b (13-26°C)

What grand cape primrose's hardiness rating actually means

Grand 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). Grand Cape Primrose has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for grand 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 grand 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 grand 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.

Grand Cape Primrose hardiness — frequently asked questions

Is grand cape primrose cold hardy?

Grand 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. Grand 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 grand cape primrose can survive?

What hardiness zone is grand cape primrose?

Grand 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 grand 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 grand 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.