Cold hardiness & minimum temperature

Is Giant Arrowhead (Sagittaria montevidensis)cold hardy? Hardiness zone & min temp

Also called Giant Arrowhead, Aztec Arrowhead, California Arrowhead, Giant Duck Potato.

More about giant arrowhead

About Giant Arrowhead

Sagittaria montevidensis · also called Giant Arrowhead, Aztec Arrowhead · flowering

Sagittaria montevidensis is a robust emergent aquatic perennial native to South America (Uruguay, Argentina, southern Brazil) and naturalised in parts of the southern United States and California. It produces very large, arrow-shaped leaves and impressive white three-petalled flowers with dark maroon basal spots on tall racemes throughout summer and into autumn. As the tallest and most dramatic Sagittaria species in cultivation, its most important care requirement is adequate depth — plant in water 10–15 cm (4–6 in) deep with full sun for maximum size and flower production. Sagittaria species are considered non-toxic to cats and dogs.

Cold limit: USDA 7-11 · RHS H3 (15–35 °C (active growth); plants die back below 10 °C; in frost-prone areas treat as an annual or overwinter containers indoors)

What giant arrowhead's hardiness rating actually means

Giant Arrowhead 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 7-11 — 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. Giant Arrowhead shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for giant arrowhead 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 giant arrowhead go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 7-11 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 giant arrowhead 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 giant arrowhead

Giant Arrowhead 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.

Giant Arrowhead hardiness — frequently asked questions

Is giant arrowhead cold hardy?

Giant Arrowhead 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 7-11 (and sheltered UK gardens) giant arrowhead can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature giant arrowhead can survive?

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

What hardiness zone is giant arrowhead?

Giant Arrowhead is rated USDA 7-11 and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can giant arrowhead survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 7-11 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 giant arrowhead 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.