Cold hardiness & minimum temperature

Is Streptocarpus 'Polka-Dot Purple' (Streptocarpus 'Polka-Dot Purple')cold hardy? Hardiness zone & min temp

Also called Polka-Dot Cape Primrose.

More about streptocarpus 'polka-dot purple'

About Streptocarpus 'Polka-Dot Purple'

Streptocarpus 'Polka-Dot Purple' · also called Polka-Dot Cape Primrose · flowering

Streptocarpus 'Polka-Dot Purple' is a compact Cape primrose hybrid grown for purple, speckle-throated trumpet flowers held on slender stalks above strappy, quilted leaves. It blooms in flushes for much of the year in bright indirect light, dislikes wet crowns and soggy roots, and rewards a steady, slightly-dry-between-watering routine. Pet-safe per ASPCA.

Cold limit: USDA 10-11 (indoor in most US homes) · RHS H1b (16-24°C)

What streptocarpus 'polka-dot purple''s hardiness rating actually means

Streptocarpus 'Polka-Dot Purple' 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 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 'Polka-Dot Purple' has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

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

Streptocarpus 'Polka-Dot Purple' hardiness — frequently asked questions

Is streptocarpus 'polka-dot purple' cold hardy?

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

What is the minimum temperature streptocarpus 'polka-dot purple' can survive?

What hardiness zone is streptocarpus 'polka-dot purple'?

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

Can streptocarpus 'polka-dot purple' 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 'polka-dot purple' 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.