Cold hardiness & minimum temperature

Is Annual Rainbow Plant (Byblis liniflora)cold hardy? Hardiness zone & min temp

Also called annual rainbow plant, rainbow plant.

More about annual rainbow plant

About Annual Rainbow Plant

Byblis liniflora · also called annual rainbow plant, rainbow plant · houseplant

A dazzling annual carnivore from tropical northern Australia and southern New Guinea, smothered in glistening mucilage-tipped glands that scatter rainbow light. Grows quickly from seed to 10–30 cm, flowering profusely with violet blooms before setting seed and dying. Grows one full season then must be restarted from seed each year.

Cold limit: USDA 10–12 (frost-free only; treated as an annual everywhere) · RHS H1a (18–38°C)

What annual rainbow plant's hardiness rating actually means

Annual Rainbow Plant 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 H1a means: Tropical — needs a heated room or greenhouse; no frost tolerance whatsoever. On the US scale that maps to USDA 10–12 (frost-free only; treated as an annual everywhere) — 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 above about 15 °C (warm, never cold). Annual Rainbow Plant has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for annual rainbow plant as it gets too cold:

Below about above about 15 °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 annual rainbow plant go outside or overwinter — and where?

It can holiday outdoors in summer once nights are reliably above above 15 °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 annual rainbow plant can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1a figure above.

Annual Rainbow Plant hardiness — frequently asked questions

Is annual rainbow plant cold hardy?

Annual Rainbow Plant 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. Annual Rainbow Plant can only live outside year-round in genuinely frost-free climates (roughly USDA 10–12 (frost-free only; treated as an annual everywhere)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature annual rainbow plant can survive?

Minimum survivable temperature is roughly above about 15 °C (warm, never cold). Annual Rainbow Plant has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

What hardiness zone is annual rainbow plant?

Annual Rainbow Plant is rated USDA 10–12 (frost-free only; treated as an annual everywhere) and RHS H1a — Tropical — needs a heated room or greenhouse; no frost tolerance whatsoever.

Can annual rainbow plant survive winter outside?

It can holiday outdoors in summer once nights are reliably above above 15 °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 annual rainbow plant below its minimum temperature?

Below about above about 15 °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.