Cold hardiness & minimum temperature

Is Zulu Spurflower (Plectranthus zuluensis)cold hardy? Hardiness zone & min temp

Also called Zulu Spurflower, Zulu Spur Flower.

More about zulu spurflower

About Zulu Spurflower

Plectranthus zuluensis · also called Zulu Spurflower, Zulu Spur Flower · flowering

Plectranthus zuluensis is an upright to sprawling, soft-wooded shrub native to the coastal forests and forest margins of KwaZulu-Natal, South Africa, grown for its striking display of bright lime-green, velvety leaves and graceful racemes of blue to pale mauve tubular flowers from late spring through summer. It thrives in shady garden spots that are difficult to plant and flowers prolifically even in deep shade, making it a valuable landscape plant. The single most critical care fact is that it is frost-tender — any freeze will kill it outright, so it must be grown under glass or as a conservatory plant in the UK and all but the mildest US climates. Not individually listed by ASPCA; treat as mildly toxic due to aromatic essential oil content.

Cold limit: USDA 9a–11b (indoor in most climates) · RHS H2 (5–28°C)

Watch for — Frost damage: Even a light frost will blacken and kill the soft stems; in the UK bring plants under glass by mid-October and do not return them outdoors until all frost risk has passed in late spring.

What zulu spurflower's hardiness rating actually means

Zulu Spurflower is half-hardy (RHS H2). 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 H2 means: Tender — survives a frost-free greenhouse or a very mild, sheltered spot. On the US scale that maps to USDA 9a–11b (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 1 to 5 °C — tolerates cold but no real frost. Zulu Spurflower shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for zulu spurflower as it gets too cold:

Down to roughly about 1 to 5 °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 zulu spurflower go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 9a–11b (indoor in most climates) 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 zulu spurflower can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H2 figure above.

Frost protection for borderline zulu spurflower

Zulu Spurflower 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.

Zulu Spurflower hardiness — frequently asked questions

Is zulu spurflower cold hardy?

Zulu Spurflower is half-hardy (RHS H2). 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 9a–11b (indoor in most climates) (and sheltered UK gardens) zulu spurflower can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature zulu spurflower can survive?

Minimum survivable temperature is roughly about 1 to 5 °C — tolerates cold but no real frost. Zulu Spurflower shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is zulu spurflower?

Zulu Spurflower is rated USDA 9a–11b (indoor in most climates) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can zulu spurflower survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9a–11b (indoor in most climates) 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 zulu spurflower 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.