Cold hardiness & minimum temperature

Is Hot Water Plant (Achimenes longiflora)cold hardy? Hardiness zone & min temp

Also called Hot Water Plant, Magic Flower, Nut Orchid.

More about hot water plant

About Hot Water Plant

Achimenes longiflora · also called Hot Water Plant, Magic Flower · houseplant

Hot Water Plant is a delightful summer-flowering gesneriad producing trumpet-shaped lavender, purple, or white flowers on cascading stems from small scaly rhizomes. It is nicknamed 'hot water plant' because warm water was historically used to start it into growth. ASPCA non-toxic and pet-safe.

Cold limit: USDA 10-12 (grown from rhizomes as tender perennials in most zones) · RHS H1c (18-27°C)

Watch for — Failure to emerge in spring: Rhizomes require warmth (above 18°C) to break dormancy. If pots are kept in a cold space, growth will be delayed. Apply warm water and move to a warm, bright spot to encourage sprouting.

What hot water plant's hardiness rating actually means

Hot Water 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 H1c means: Warm-temperate — can summer outdoors but must come in well before the first frost. On the US scale that maps to USDA 10-12 (grown from rhizomes as tender perennials in most 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 5 °C (and never frost). Hot Water Plant has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for hot water plant as it gets too cold:

Below about about 5 °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 hot water plant go outside or overwinter — and where?

It can holiday outdoors in summer once nights are reliably above 5 °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 hot water plant can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1c figure above.

Hot Water Plant hardiness — frequently asked questions

Is hot water plant cold hardy?

Hot Water 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. Hot Water Plant can only live outside year-round in genuinely frost-free climates (roughly USDA 10-12 (grown from rhizomes as tender perennials in most zones)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature hot water plant can survive?

Minimum survivable temperature is roughly about 5 °C (and never frost). Hot Water Plant has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

What hardiness zone is hot water plant?

Hot Water Plant is rated USDA 10-12 (grown from rhizomes as tender perennials in most zones) and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can hot water plant survive winter outside?

It can holiday outdoors in summer once nights are reliably above 5 °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 hot water plant below its minimum temperature?

Below about about 5 °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.