Cold hardiness & minimum temperature

Is Salvinia molesta (Salvinia molesta)cold hardy? Hardiness zone & min temp

Also called Giant Salvinia, Kariba Weed, Aquarium Watermoss.

More about salvinia molesta

About Salvinia molesta

Salvinia molesta · also called Giant Salvinia, Kariba Weed · houseplant

Salvinia molesta is a larger, more vigorous floating fern famous for the eggbeater-shaped split hairs on its leaves that make it almost impossible to wet. Sometimes used in aquariums, it is one of the world's most damaging aquatic weeds, capable of forming thick floating rafts. Grow only in fully contained systems and never release it.

Cold limit: USDA 9-11 (frost-sensitive; killed by hard freeze, so it is seasonal outdoors and indoor-contained in most of the US) · RHS H2 (20-30°C)

Watch for — Stunted flat growth: In low light or cold water it stays in the small flat juvenile form. This is harmless but signals conditions below its preferred warm, bright range.

What salvinia molesta's hardiness rating actually means

Salvinia molesta 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 9-11 (frost-sensitive; killed by hard freeze, so it is seasonal outdoors and indoor-contained in most of the US) — 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. Salvinia molesta shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for salvinia molesta 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 salvinia molesta go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (frost-sensitive; killed by hard freeze, so it is seasonal outdoors and indoor-contained in most of the US) 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 salvinia molesta 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 salvinia molesta

Salvinia molesta 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.

Salvinia molesta hardiness — frequently asked questions

Is salvinia molesta cold hardy?

Salvinia molesta 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 9-11 (frost-sensitive; killed by hard freeze, so it is seasonal outdoors and indoor-contained in most of the US) (and sheltered UK gardens) salvinia molesta can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature salvinia molesta can survive?

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

What hardiness zone is salvinia molesta?

Salvinia molesta is rated USDA 9-11 (frost-sensitive; killed by hard freeze, so it is seasonal outdoors and indoor-contained in most of the US) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can salvinia molesta survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (frost-sensitive; killed by hard freeze, so it is seasonal outdoors and indoor-contained in most of the US) 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 salvinia molesta 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.