Cold hardiness & minimum temperature

Is Hill Wax Plant (Hoya collina)cold hardy? Hardiness zone & min temp

Also called Hill wax plant, Wax plant.

More about hill wax plant

About Hill Wax Plant

Hoya collina · also called Hill wax plant, Wax plant · tropical

Hoya collina is a compact epiphytic climber native to the hill forests of northeastern New Guinea, recognised by its fleshy, smooth, rounded leaves (3.5–5.5 cm long) and small pale yellow flowers about 0.8 cm across that carry a sweet aroma and produce abundant nectar. A popular clone features deep green leaves speckled with silver. It prefers bright indirect light and should be allowed to dry slightly between waterings to avoid the root rot to which it is susceptible. The ASPCA classifies the Hoya genus as non-toxic to cats, dogs, and horses.

Cold limit: USDA 11–12 (indoor in most climates) · RHS H1b (16–28 °C)

What hill wax plant's hardiness rating actually means

Hill 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 11–12 (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). Hill Wax Plant has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for hill 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 hill 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 hill 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.

Hill Wax Plant hardiness — frequently asked questions

Is hill wax plant cold hardy?

Hill 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. Hill Wax Plant can only live outside year-round in genuinely frost-free climates (roughly USDA 11–12 (indoor in most climates)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature hill wax plant can survive?

What hardiness zone is hill wax plant?

Hill Wax Plant is rated USDA 11–12 (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 hill 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 hill 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.