Cold hardiness & minimum temperature

Is Red Clockvine (Thunbergia coccinea)cold hardy? Hardiness zone & min temp

Also called Red Clockvine, Scarlet Clockvine, Scarlet Thunbergia.

More about red clockvine

About Red Clockvine

Thunbergia coccinea · also called Red Clockvine, Scarlet Clockvine · tropical

Thunbergia coccinea is a stunning tropical vine from the Indian subcontinent bearing pendant racemes of scarlet-orange tubular flowers with a yellow throat from autumn through spring. Fast-growing and hummingbird-attracting, it excels on pergolas and large trellises in warm climates or as a spectacular conservatory climber in cooler regions.

Cold limit: USDA 10-12 · RHS H1b (18–35 °C)

Watch for — Cold damage under glass: Even brief temperature drops below 10 °C cause leaf yellowing and stem dieback. Maintain a minimum night temperature of 13–15 °C in winter and keep the plant away from draughty vents or cold glass.

What red clockvine's hardiness rating actually means

Red Clockvine 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 — 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). Red Clockvine has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

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

Red Clockvine hardiness — frequently asked questions

Is red clockvine cold hardy?

Red Clockvine 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. Red Clockvine can only live outside year-round in genuinely frost-free climates (roughly USDA 10-12); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature red clockvine can survive?

What hardiness zone is red clockvine?

Red Clockvine is rated USDA 10-12 and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can red clockvine 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 red clockvine 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.