Cold hardiness & minimum temperature

Is Twinspur (Diascia barberae)cold hardy? Hardiness zone & min temp

Also called Twinspur, Barbera twinspur.

More about twinspur

About Twinspur

Diascia barberae · also called Twinspur, Barbera twinspur · flowering

Twinspur is a dainty South African annual or short-lived perennial producing masses of small pink to coral tubular flowers with characteristic twin spurs on slender branching stems. It excels in cool-season gardens, window boxes, and hanging baskets, blooming most prolifically in spring and autumn when temperatures remain mild.

Cold limit: USDA 7-9 · RHS H3 (5–22°C)

Watch for — Summer dormancy / heat stress: Diascia barberae often goes dormant or stops flowering when temperatures consistently exceed 25°C. Cut back by half, reduce watering, and flowering typically resumes in cooler autumn weather.

What twinspur's hardiness rating actually means

Twinspur is half-hardy (RHS H3). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Its RHS rating of H3 means: Half-hardy — comes through mild UK winters outside but is killed by a hard freeze. On the US scale that maps to USDA 7-9 — 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 −5 to 1 °C — a light, short frost only. Twinspur shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for twinspur as it gets too cold:

Down to roughly about −5 to 1 °C it copes, especially if dry and sheltered.
A sustained hard frost collapses the top growth; whether it returns depends on whether the roots, crown or tubers froze.
Wet cold is far more lethal than dry cold for this plant — soggy, frozen soil is the usual killer.

Can twinspur go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 7-9 or a frost-free UK microclimate.
In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter.
A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

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 twinspur can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H3 figure above.

Frost protection for borderline twinspur

Twinspur is right on a hardiness edge in many gardens, so if you are pushing it, these measures buy it the margin it needs:

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost.
Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse.
Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones.
Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.

Twinspur hardiness — frequently asked questions

Is twinspur cold hardy?

Twinspur is half-hardy (RHS H3). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Borderline outdoors. In its mild end of USDA 7-9 (and sheltered UK gardens) twinspur can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature twinspur can survive?

Minimum survivable temperature is roughly about −5 to 1 °C — a light, short frost only. Twinspur shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is twinspur?

Twinspur is rated USDA 7-9 and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can twinspur survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 7-9 or a frost-free UK microclimate. In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter. A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

How do I protect twinspur from frost?

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost. Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse. Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones. Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.