Cold hardiness & minimum temperature

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

Also called large-flowered achimenes, orchid pansy.

More about achimenes grandiflora

About Achimenes grandiflora

Achimenes grandiflora · also called large-flowered achimenes, orchid pansy · flowering

Achimenes grandiflora, the large-flowered hot water plant, is a Mexican gesneriad bearing showy purple-magenta blooms with white throats across summer. It grows from tiny scaly rhizomes, demanding warmth, steady moisture, and humid air to flower freely. After bloom it dies back to dormant rhizomes that are stored dry and cool, then restarted with warm water in spring.

Cold limit: USDA 9-11 (lifted/stored dormant elsewhere) · RHS H1b (18-27°C)

Watch for — Premature dormancy: Letting the soil dry out, cold drafts, or a sudden chill can trigger early die-back. Keep warmth and steady moisture through summer to prolong flowering.

What achimenes grandiflora's hardiness rating actually means

Achimenes grandiflora 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 9-11 (lifted/stored dormant elsewhere) — 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 grandiflora has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

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

Achimenes grandiflora hardiness — frequently asked questions

Is achimenes grandiflora cold hardy?

Achimenes grandiflora 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 grandiflora can only live outside year-round in genuinely frost-free climates (roughly USDA 9-11 (lifted/stored dormant elsewhere)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature achimenes grandiflora can survive?

What hardiness zone is achimenes grandiflora?

Achimenes grandiflora is rated USDA 9-11 (lifted/stored dormant elsewhere) and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can achimenes grandiflora 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 grandiflora 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.