Cold hardiness & minimum temperature

Is Japanese Arrowhead (Sagittaria japonica)cold hardy? Hardiness zone & min temp

Also called Japanese Arrowhead, Arrowhead Water Plant, Kuwai.

More about japanese arrowhead

About Japanese Arrowhead

Sagittaria japonica · also called Japanese Arrowhead, Arrowhead Water Plant · edible

Japanese Arrowhead is an aquatic perennial grown for its arrow-shaped leaves and edible corms, prized in Japanese and Chinese cuisine. It thrives in shallow ponds, bog gardens, or containers of standing water in full sun. Starchy corms are harvested in autumn and can be roasted, boiled, or stir-fried. Hardy in temperate climates.

Cold limit: USDA 5–11 · RHS H5 (5–30°C)

What japanese arrowhead's hardiness rating actually means

Yes — japanese arrowhead is genuinely cold hardy. Rated RHS H5 and USDA 5–11, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H5 means: Hardy in most of the UK and in cold winters. On the US scale that maps to USDA 5–11 — 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 −15 to −10 °C. Japanese Arrowhead is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for japanese arrowhead as it gets too cold:

It tolerates winter lows to about −15 to −10 °C once established.
Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root.
First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.

Can japanese arrowhead go outside or overwinter — and where?

Plant it out within USDA 5–11 and it overwinters with little or no help.
It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy.
The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

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 japanese arrowhead can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Japanese Arrowhead hardiness — frequently asked questions

Is japanese arrowhead cold hardy?

Yes — japanese arrowhead is genuinely cold hardy. Rated RHS H5 and USDA 5–11, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Japanese Arrowhead is hardy across USDA 5–11; it belongs in the ground or a frost-proof container, not on a windowsill, and many types actively need a cold winter to perform.

What is the minimum temperature japanese arrowhead can survive?

Minimum survivable temperature is roughly about −15 to −10 °C. Japanese Arrowhead is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is japanese arrowhead?

Japanese Arrowhead is rated USDA 5–11 and RHS H5 — Hardy in most of the UK and in cold winters.

Can japanese arrowhead survive winter outside?

Plant it out within USDA 5–11 and it overwinters with little or no help. It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy. The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

What happens to japanese arrowhead below its minimum temperature?

It tolerates winter lows to about −15 to −10 °C once established. Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root. First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.