Cold hardiness & minimum temperature

Is Free-flowering Streptocarpus (Streptocarpus floribundus)cold hardy? Hardiness zone & min temp

Also called Free-flowering Streptocarpus, Kranskop Streptocarpus.

More about free-flowering streptocarpus

About Free-flowering Streptocarpus

Streptocarpus floribundus · also called Free-flowering Streptocarpus, Kranskop Streptocarpus · houseplant

Streptocarpus floribundus is a rare, threatened perennial herb native to the doleritic cliff faces of Kranskop in KwaZulu-Natal, South Africa, where it grows in cool, shaded, moist crevices. It produces masses of mauve-purple, tubular flowers — hence the species epithet floribundus, meaning 'flowering freely' — mainly in early summer. The most critical care requirement is avoiding overwatering, as this plant is extremely sensitive to waterlogged roots despite needing consistently moist conditions. Cape primrose (Streptocarpus) is listed by the ASPCA as non-toxic to cats and dogs.

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

What free-flowering streptocarpus's hardiness rating actually means

Free-flowering Streptocarpus 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). Free-flowering Streptocarpus has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

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

Free-flowering Streptocarpus hardiness — frequently asked questions

Is free-flowering streptocarpus cold hardy?

Free-flowering Streptocarpus 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. Free-flowering Streptocarpus 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 free-flowering streptocarpus can survive?

What hardiness zone is free-flowering streptocarpus?

Free-flowering Streptocarpus 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 free-flowering streptocarpus 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 free-flowering streptocarpus 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.