Cold hardiness & minimum temperature

Is Lobster Flower (Plectranthus neochilus)cold hardy? Hardiness zone & min temp

Also called Lobster Flower, Blue Coleus, Spur Flower.

More about lobster flower

About Lobster Flower

Plectranthus neochilus · also called Lobster Flower, Blue Coleus · flowering

Plectranthus neochilus is a low-growing, mat-forming, semi-succulent perennial native to southern Africa, instantly recognisable by its lime-green, broad leaves with coppery-purple undersides and its strong, pungent aroma that is widely used as a natural cat and dog deterrent in gardens. It produces upright spikes of soft purple-blue tubular flowers through much of the growing season. The most important care fact is that it is remarkably drought tolerant due to its succulent stems, and overwatering is the primary cause of failure — water only when the soil is fully dry. Multiple sources classify the genus pattern as non-toxic to dogs and cats, and Mountain Crest Gardens specifically lists P. neochilus as pet-safe.

Cold limit: USDA 9a–10b · RHS H2 (7–30°C)

What lobster flower's hardiness rating actually means

Lobster Flower 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–10b — 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. Lobster Flower shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for lobster flower 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 lobster flower go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 9a–10b 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 lobster flower 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 lobster flower

Lobster Flower 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.

Lobster Flower hardiness — frequently asked questions

Is lobster flower cold hardy?

Lobster Flower 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–10b (and sheltered UK gardens) lobster flower can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature lobster flower can survive?

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

What hardiness zone is lobster flower?

Lobster Flower is rated USDA 9a–10b and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can lobster flower survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9a–10b 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 lobster flower 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.