Cold hardiness & minimum temperature

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

Also called hot water plant, Achimenes, widow's tears.

More about achimenes

About Achimenes

Achimenes longiflora · also called hot water plant, Achimenes · flowering

Achimenes longiflora, the hot water plant, is a tropical rhizomatous gesneriad that explodes into violet-blue, trumpet-shaped flowers all summer above soft, hairy leaves. A relative of the African violet, it grows from tiny scaly rhizomes, blooms profusely in warmth and bright indirect light, then dies back to overwinter dormant. Steady warmth and even moisture are key, as a check in growth can stall flowering entirely.

Cold limit: USDA 10-11 (indoor / summer container in most US and UK; rhizomes stored dry over winter) · RHS H1b (18-27°C)

Watch for — Premature dormancy: Letting the plant dry out, chill, or experience cold water mid-season can trigger early die-back. Keep warmth and moisture even with tepid water throughout summer.

What achimenes's hardiness rating actually means

Achimenes 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 10-11 (indoor / summer container in most US and UK; rhizomes stored dry over winter) — 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). Achimenes has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

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

Achimenes hardiness — frequently asked questions

Is achimenes cold hardy?

Achimenes 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. Achimenes can only live outside year-round in genuinely frost-free climates (roughly USDA 10-11 (indoor / summer container in most US and UK; rhizomes stored dry over winter)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature achimenes can survive?

Minimum survivable temperature is roughly about 10 °C (sustained cold below this is damaging). Achimenes has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

What hardiness zone is achimenes?

Achimenes is rated USDA 10-11 (indoor / summer container in most US and UK; rhizomes stored dry over winter) and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can achimenes 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 achimenes 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.