Cold hardiness & minimum temperature

Is Nun's Orchid (Phaius tankervilleae)cold hardy? Hardiness zone & min temp

Also called Swamp Orchid, Veiled Nun Orchid.

More about nun's orchid

About Nun's Orchid

Phaius tankervilleae · also called Swamp Orchid, Veiled Nun Orchid · flowering

Phaius tankervilleae is a robust terrestrial orchid from Asia and the Pacific, sending up tall spikes of large, reddish-brown flowers backed with white and a rosy, trumpet-shaped lip. Unlike epiphytic orchids it grows in rich, moisture-retentive soil, wanting bright shade, warmth, steady water and feeding in growth, and is among the easiest orchids to grow as a houseplant or shaded garden plant.

Cold limit: USDA 9-11 (root-hardy in mild zones with protection; indoor elsewhere) · RHS H1b (16-29°C)

What nun's orchid's hardiness rating actually means

Nun's Orchid 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 (root-hardy in mild zones with protection; indoor 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). Nun's Orchid has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

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

Nun's Orchid hardiness — frequently asked questions

Is nun's orchid cold hardy?

Nun's Orchid 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. Nun's Orchid can only live outside year-round in genuinely frost-free climates (roughly USDA 9-11 (root-hardy in mild zones with protection; indoor elsewhere)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature nun's orchid can survive?

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

What hardiness zone is nun's orchid?

Nun's Orchid is rated USDA 9-11 (root-hardy in mild zones with protection; indoor elsewhere) and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can nun's orchid 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 nun's orchid 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.