Cold hardiness & minimum temperature

Is Fragrant Stomatium (Stomatium suaveolens)cold hardy? Hardiness zone & min temp

Also called Fragrant Stomatium, Night-blooming Iceplant.

More about fragrant stomatium

About Fragrant Stomatium

Stomatium suaveolens · also called Fragrant Stomatium, Night-blooming Iceplant · houseplant

Stomatium suaveolens is a dwarf clump-forming mesemb from the Northern Cape of South Africa, prized for its intensely sweet-scented yellow flowers that open at dusk. A winter grower that tolerates surprising cold in its Sutherland form. Grow in a gritty, free-draining mix, keep almost dry in summer, and site near a window for evening fragrance.

Cold limit: USDA 9b–11 · RHS H2 (4–30°C)

Watch for — Failure to flower: Flowers open in the evening, so they can be missed. More importantly, insufficient light or incorrect watering cycles (not giving the plant a distinct dry summer rest) prevents bud formation. Ensure a clear seasonal shift between dry-summer and wetter-winter regimes.

What fragrant stomatium's hardiness rating actually means

Fragrant Stomatium 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 9b–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 1 to 5 °C — tolerates cold but no real frost. Fragrant Stomatium shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for fragrant stomatium 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 fragrant stomatium go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 9b–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 fragrant stomatium 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 fragrant stomatium

Fragrant Stomatium 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.

Fragrant Stomatium hardiness — frequently asked questions

Is fragrant stomatium cold hardy?

Fragrant Stomatium 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 9b–11 (and sheltered UK gardens) fragrant stomatium can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature fragrant stomatium can survive?

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

What hardiness zone is fragrant stomatium?

Fragrant Stomatium is rated USDA 9b–11 and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can fragrant stomatium survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9b–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 fragrant stomatium 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.