Cold hardiness & minimum temperature

Is Prostrate Rosemary (Salvia rosmarinus 'Prostratus')cold hardy? Hardiness zone & min temp

Also called Creeping Rosemary, Trailing Rosemary.

More about prostrate rosemary

About Prostrate Rosemary

Salvia rosmarinus 'Prostratus' · also called Creeping Rosemary, Trailing Rosemary · herb

Prostrate rosemary is a low, spreading form of culinary rosemary that cascades over walls, banks, and pot edges, carrying the same needle leaves, blue spring flowers, and aromatic, kitchen-ready foliage. It loves full sun and sharp drainage, tolerates drought, but is less cold-hardy than upright cultivars and dislikes wet winter soil.

Cold limit: USDA 8-10 (less hardy than upright rosemary; protect or move under cover in colder zones) · RHS H3 (10-27°C)

Watch for — Winter root rot: Cold, wet soil rots the roots of this less-hardy form; ensure very sharp drainage and reduce winter watering, or overwinter pots under cover.

What prostrate rosemary's hardiness rating actually means

Prostrate Rosemary 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 8-10 (less hardy than upright rosemary; protect or move under cover in colder zones) — 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. Prostrate Rosemary shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for prostrate rosemary 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 prostrate rosemary go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-10 (less hardy than upright rosemary; protect or move under cover in colder zones) 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 prostrate rosemary 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 prostrate rosemary

Prostrate Rosemary 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.

Prostrate Rosemary hardiness — frequently asked questions

Is prostrate rosemary cold hardy?

Prostrate Rosemary 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 8-10 (less hardy than upright rosemary; protect or move under cover in colder zones) (and sheltered UK gardens) prostrate rosemary can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature prostrate rosemary can survive?

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

What hardiness zone is prostrate rosemary?

Prostrate Rosemary is rated USDA 8-10 (less hardy than upright rosemary; protect or move under cover in colder zones) and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can prostrate rosemary survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-10 (less hardy than upright rosemary; protect or move under cover in colder zones) 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 prostrate rosemary 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.