Cold hardiness & minimum temperature

Is Hoya (Hoya carnosa)cold hardy? Hardiness zone & min temp

Also called wax plant, porcelain flower, honey plant.

About Hoya

Hoya carnosa · also called wax plant, porcelain flower · flowering

Hoya is a vining tropical from Southeast Asia and Australia grown for its waxy leaves and clusters of fragrant star-shaped flowers. It is forgiving of neglect and rewards patience with long-lived blooms. Pet-safe by ASPCA standards.

Hoya carnosa is a perennial epiphytic climber native to East and Southeast Asia (including southern China, Japan and Taiwan) with populations in Australia, naturally scrambling over trees rather than rooting in soil.

Long-lived and slow to mature into flowering size, climbing by twining stems; it is listed by the ASPCA as non-toxic to cats and dogs, making it a safe choice for pet households.

Cold limit: USDA 10-12 (indoor-only in most US homes) · RHS H1b (18-27°C)

Sources: plants.ces.ncsu.edu, en.wikipedia.org, gardenia.net

What hoya's hardiness rating actually means

Hoya 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-only in most US homes) — 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). Hoya has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

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

Hoya hardiness — frequently asked questions

Is hoya cold hardy?

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

What is the minimum temperature hoya can survive?

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

What hardiness zone is hoya?

Hoya is rated USDA 10-12 (indoor-only in most US homes) and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can hoya 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 hoya 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.