Cold hardiness & minimum temperature

Is Sagittaria platyphylla (Sagittaria platyphylla)cold hardy? Hardiness zone & min temp

Also called broadleaf arrowhead, giant sagittaria.

More about sagittaria platyphylla

About Sagittaria platyphylla

Sagittaria platyphylla · also called broadleaf arrowhead, giant sagittaria · tropical

Sagittaria platyphylla, often sold as giant sagittaria, is a hardy rosette aquatic with broad, strap-like green leaves. Robust and undemanding, it grows in low to high light without CO2 and spreads by runners to form clumps or a tall foreground-to-midground lawn. Note it is an invasive weed in some regions, so dispose of trimmings responsibly.

Cold limit: USDA Subtropical to warm-temperate; marginal-hardy outdoors in mild zones, kept in heated aquaria elsewhere (18-28°C)

What sagittaria platyphylla's hardiness rating actually means

Sagittaria platyphylla is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Its RHS rating of H1b means: Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season. On the US scale that maps to USDA Subtropical to warm-temperate; marginal-hardy outdoors in mild zones, kept in heated aquaria elsewhere — 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 10 °C (sustained cold below this is damaging). Sagittaria platyphylla has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for sagittaria platyphylla as it gets too cold:

Below about about 10 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches.
A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover.
Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.

Can sagittaria platyphylla go outside or overwinter — and where?

It can holiday outdoors in summer once nights are reliably above 10 °C, in shade or dappled light, hardened off gradually.
Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C.
It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.

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 sagittaria platyphylla can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1b figure above.

Sagittaria platyphylla hardiness — frequently asked questions

Is sagittaria platyphylla cold hardy?

Sagittaria platyphylla is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Indoor-only in almost every home. Sagittaria platyphylla can only live outside year-round in genuinely frost-free climates (roughly USDA Subtropical to warm-temperate; marginal-hardy outdoors in mild zones, kept in heated aquaria elsewhere); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature sagittaria platyphylla can survive?

What hardiness zone is sagittaria platyphylla?

Sagittaria platyphylla is rated USDA Subtropical to warm-temperate; marginal-hardy outdoors in mild zones, kept in heated aquaria elsewhere and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can sagittaria platyphylla survive winter outside?

It can holiday outdoors in summer once nights are reliably above 10 °C, in shade or dappled light, hardened off gradually. Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C. It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.

What happens to sagittaria platyphylla below its minimum temperature?

Below about about 10 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches. A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover. Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.