Cold hardiness & minimum temperature

Is Blue Star Water Lily (Nymphaea nouchali var. caerulea)cold hardy? Hardiness zone & min temp

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

More about blue star water lily

About Blue Star Water Lily

Nymphaea nouchali var. caerulea · also called Blue Star Water Lily, Star Lotus · flowering

Native to South and Southeast Asia (India, Sri Lanka, Bangladesh), Nymphaea stellata is a day-blooming tropical water lily that produces star-shaped flowers in shades of blue, violet, and white above floating pads. It requires full sun, warm water temperatures of 70–85 °F (21–29 °C), and nutrient-rich aquatic soil; moving rhizomes indoors before frost is the single most critical winter care step outside USDA Zone 10. The ASPCA lists Nymphaea odorata (same genus) as non-toxic, but the genus can cause mild gastrointestinal upset if consumed in quantity; classified as mildly-toxic as a precaution.

Cold limit: USDA 10-12 (overwinter rhizomes indoors in colder zones) · RHS H1b (21–32 °C (active growth); rhizomes can survive to 10 °C if kept damp)

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 10-12 (overwinter rhizomes indoors in colder zones) — 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 10-12 (overwinter rhizomes indoors in colder zones)); 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 10-12 (overwinter rhizomes indoors in colder zones) 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.