Cold hardiness & minimum temperature

Is MacGillivray's Wax Plant (Hoya macgillivrayi)cold hardy? Hardiness zone & min temp

Also called MacGillivray's wax plant, Red hoya, MacGillivray's hoya.

More about macgillivray's wax plant

About MacGillivray's Wax Plant

Hoya macgillivrayi · also called MacGillivray's wax plant, Red hoya · tropical

Hoya macgillivrayi is a fast-growing, twining climber endemic to the Iron Range and McIlwraith Range of Cape York Peninsula, Queensland, Australia, where it scrambles through rainforest at the forest edge. It produces some of the largest flowers in the genus — up to 6 cm across — in rich burgundy red, with a glorious citrus-and-gardenia fragrance that can last up to three weeks; the most important care tip is to keep it slightly pot-bound and reduce watering in winter to encourage prolific flowering. The ASPCA lists the Hoya genus as non-toxic to cats and dogs.

Cold limit: USDA 10-12 (indoor in most climates) · RHS H1b (15–32°C)

What macgillivray's wax plant's hardiness rating actually means

MacGillivray's Wax 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 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 10-12 (indoor in most climates) — 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). MacGillivray's Wax Plant has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

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

MacGillivray's Wax Plant hardiness — frequently asked questions

Is macgillivray's wax plant cold hardy?

MacGillivray's Wax 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. MacGillivray's Wax Plant can only live outside year-round in genuinely frost-free climates (roughly USDA 10-12 (indoor in most climates)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature macgillivray's wax plant can survive?

What hardiness zone is macgillivray's wax plant?

MacGillivray's Wax Plant is rated USDA 10-12 (indoor in most climates) and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can macgillivray's wax plant 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 macgillivray's wax plant 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.