Cold hardiness & minimum temperature

Is Streptocarpus 'Purple Haze' (Streptocarpus 'Purple Haze')cold hardy? Hardiness zone & min temp

Also called Cape primrose, purple haze streptocarpus.

More about streptocarpus 'purple haze'

About Streptocarpus 'Purple Haze'

Streptocarpus 'Purple Haze' · also called Cape primrose, purple haze streptocarpus · flowering

Streptocarpus 'Purple Haze' is a compact Cape primrose cultivar carrying clouds of rich violet-purple flowers veined with deeper purple over rosettes of soft, quilted leaves. Like all Streptocarpus it thrives in bright indirect light with careful watering and high-potash feeding, flowering for much of the year. The ASPCA lists Cape primrose as non-toxic to pets.

Cold limit: USDA 10-11 (indoor in most US and UK homes) · RHS H1b (15-24°C)

Watch for — Soft, drooping leaves: Cold exposure below ~12°C or sudden draughts. Keep in a stable, warm position away from cold glass.

What streptocarpus 'purple haze''s hardiness rating actually means

Streptocarpus 'Purple Haze' 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 (indoor in most US and UK homes) — 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). Streptocarpus 'Purple Haze' has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for streptocarpus 'purple haze' 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 streptocarpus 'purple haze' 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 streptocarpus 'purple haze' can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1b figure above.

Streptocarpus 'Purple Haze' hardiness — frequently asked questions

Is streptocarpus 'purple haze' cold hardy?

Streptocarpus 'Purple Haze' 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. Streptocarpus 'Purple Haze' can only live outside year-round in genuinely frost-free climates (roughly USDA 10-11 (indoor in most US and UK homes)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature streptocarpus 'purple haze' can survive?

What hardiness zone is streptocarpus 'purple haze'?

Streptocarpus 'Purple Haze' is rated USDA 10-11 (indoor in most US and UK homes) and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can streptocarpus 'purple haze' 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 streptocarpus 'purple haze' 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.