Cold hardiness & minimum temperature

Is Muir's Sage (Salvia muirii)cold hardy? Hardiness zone & min temp

Also called Muir's Sage, Cape Sage, Wild Sage, Vicks Sage.

More about muir's sage

About Muir's Sage

Salvia muirii · also called Muir's Sage, Cape Sage · flowering

Salvia muirii is a small, twiggy, evergreen shrub endemic to the southern Cape coast of South Africa, native to rocky coastal scrub between the Cape of Good Hope and Mossel Bay. It produces intense blue flowers from mid-summer to autumn and bears leathery, grey-green leaves that when crushed release a distinctive menthol-like scent reminiscent of Vicks VapoRub. The most important care fact is providing sharp drainage and full sun; once established, it is highly drought tolerant and frost hardy for a South African shrub. The genus Salvia is listed as non-toxic to cats, dogs, and horses by the ASPCA.

Cold limit: USDA 7b-11 · RHS H3 (-4–35°C)

Watch for — Dieback from waterlogging: Salvia muirii is highly sensitive to wet roots; waterlogged or poorly drained soil quickly causes stem dieback and root rot, particularly in winter — raised planting is recommended in heavy soils.

What muir's sage's hardiness rating actually means

Muir's Sage 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 7b-11 — 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. Muir's Sage shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for muir's sage 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 muir's sage go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 7b-11 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 muir's sage 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 muir's sage

Muir's Sage 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.

Muir's Sage hardiness — frequently asked questions

Is muir's sage cold hardy?

Muir's Sage 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 7b-11 (and sheltered UK gardens) muir's sage can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature muir's sage can survive?

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

What hardiness zone is muir's sage?

Muir's Sage is rated USDA 7b-11 and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can muir's sage survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 7b-11 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 muir's sage 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.