Cold hardiness & minimum temperature

Is Vallisneria gigantea (Vallisneria gigantea)cold hardy? Hardiness zone & min temp

Also called giant vallis, jungle vallis.

More about vallisneria gigantea

About Vallisneria gigantea

Vallisneria gigantea · also called giant vallis, jungle vallis · tropical

Vallisneria gigantea, giant or jungle vallis, is the largest tape grass in the hobby, producing very long, broad ribbon leaves that fill the back of big aquariums and trail across the surface. It spreads strongly by runners into a swaying jungle backdrop and is hardy, fast-growing, and a vigorous oxygenator for tall tanks.

Cold limit: USDA 9-11 (warm-water tropical; not frost-hardy) (20-28°C)

What vallisneria gigantea's hardiness rating actually means

Vallisneria gigantea 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 (warm-water tropical; not frost-hardy) — 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. Vallisneria gigantea shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for vallisneria gigantea 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 vallisneria gigantea go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (warm-water tropical; not frost-hardy) 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 vallisneria gigantea 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 vallisneria gigantea

Vallisneria gigantea 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.

Vallisneria gigantea hardiness — frequently asked questions

Is vallisneria gigantea cold hardy?

Vallisneria gigantea 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 (warm-water tropical; not frost-hardy) (and sheltered UK gardens) vallisneria gigantea can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature vallisneria gigantea can survive?

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

What hardiness zone is vallisneria gigantea?

Vallisneria gigantea is rated USDA 9-11 (warm-water tropical; not frost-hardy) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can vallisneria gigantea survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (warm-water tropical; not frost-hardy) 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 vallisneria gigantea 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.