Cold hardiness & minimum temperature

Is Blue Star Water Lily (Nymphaea stellata)cold hardy? Hardiness zone & min temp

Also called Blue Star Water Lily, Star Lotus, Blue Lotus.

More about blue star water lily

About Blue Star Water Lily

Nymphaea stellata · also called Blue Star Water Lily, Star Lotus · tropical

The Blue Star Water Lily is a graceful tropical water lily from South and Southeast Asia, bearing small-to-medium blue-violet star-shaped flowers and round to oval leaves with reddish-purple mottling. Flowering during daylight hours, it is prized in ponds and water gardens. Fast-growing in warm, sunny conditions. Mildly toxic if ingested.

Cold limit: USDA 9-12 (outdoor ponds; overwinter tubers above 10°C in colder climates) · RHS H1b (24-32°C)

Watch for — Rhizome rot: Usually caused by cold water or waterlogged heavy clay; replant in fresh aquatic compost and ensure water temperature stays above 20°C.

What blue star water lily's hardiness rating actually means

Blue Star Water Lily 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 9-12 (outdoor ponds; overwinter tubers above 10°C in colder climates) — 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). Blue Star Water Lily has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for blue star water lily 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 blue star water lily 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 blue star water lily can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1b figure above.

Blue Star Water Lily hardiness — frequently asked questions

Is blue star water lily cold hardy?

Blue Star Water Lily 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. Blue Star Water Lily can only live outside year-round in genuinely frost-free climates (roughly USDA 9-12 (outdoor ponds; overwinter tubers above 10°C in colder climates)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature blue star water lily can survive?

What hardiness zone is blue star water lily?

Blue Star Water Lily is rated USDA 9-12 (outdoor ponds; overwinter tubers above 10°C in colder climates) and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can blue star water lily 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 blue star water lily 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.