Cold hardiness & minimum temperature

Is Streptocarpus 'Harlequin Blue' (Streptocarpus 'Harlequin Blue')cold hardy? Hardiness zone & min temp

Also called Harlequin Blue Cape Primrose.

More about streptocarpus 'harlequin blue'

About Streptocarpus 'Harlequin Blue'

Streptocarpus 'Harlequin Blue' · also called Harlequin Blue Cape Primrose · flowering

Streptocarpus 'Harlequin Blue' is a free-flowering Cape Primrose cultivar with rich blue upper petals and yellow-marked lower petals above strappy green leaves. An award-worthy, compact gesneriad, it blooms for months on a bright, cool windowsill, preferring to dry slightly between waterings and avoiding hot, wet conditions. Pet-safe like its African violet relatives, it is an easygoing flowering houseplant.

Cold limit: USDA 10-11 (grown as an indoor plant) · RHS H1b (15-24°C)

What streptocarpus 'harlequin blue''s hardiness rating actually means

Streptocarpus 'Harlequin Blue' 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 (grown as an indoor plant) — 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 'Harlequin Blue' has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

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

Streptocarpus 'Harlequin Blue' hardiness — frequently asked questions

Is streptocarpus 'harlequin blue' cold hardy?

Streptocarpus 'Harlequin Blue' 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 'Harlequin Blue' can only live outside year-round in genuinely frost-free climates (roughly USDA 10-11 (grown as an indoor plant)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature streptocarpus 'harlequin blue' can survive?

What hardiness zone is streptocarpus 'harlequin blue'?

Streptocarpus 'Harlequin Blue' is rated USDA 10-11 (grown as an indoor plant) and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can streptocarpus 'harlequin blue' 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 'harlequin blue' 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.