Cold hardiness & minimum temperature

Is Haygarth's Cape Primrose (Streptocarpus haygarthii)cold hardy? Hardiness zone & min temp

Also called Haygarth's Cape Primrose, Cape Primrose.

More about haygarth's cape primrose

About Haygarth's Cape Primrose

Streptocarpus haygarthii · also called Haygarth's Cape Primrose, Cape Primrose · flowering

Streptocarpus haygarthii is a rosulate species endemic to the mist-belt forests and rocky outcrops of KwaZulu-Natal, South Africa. It bears clusters of soft lavender-pink flowers on slender scapes above a compact rosette of wrinkled, dark-green leaves. Cool nights (below 15°C) are beneficial for initiating flower buds, making temperature management the single most important factor for reliable blooming indoors. The species is non-toxic to cats and dogs per the ASPCA.

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

Watch for — Failure to bloom: This species requires a cool winter rest (nights around 10-14°C) to initiate flower buds; plants kept uniformly warm year-round rarely flower. Move to a cool room or unheated greenhouse in winter.

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

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

Concretely, for haygarth's 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 haygarth's 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 haygarth's 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.

Haygarth's Cape Primrose hardiness — frequently asked questions

Is haygarth's cape primrose cold hardy?

Haygarth'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. Haygarth's 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 haygarth's cape primrose can survive?

What hardiness zone is haygarth's cape primrose?

Haygarth's 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 haygarth's 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 haygarth's 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.