Cold hardiness & minimum temperature

Is Sweetheart plant (Hoya kerrii)cold hardy? Hardiness zone & min temp

Also called lucky heart, Valentine hoya, sweetheart hoya.

About Sweetheart plant

Hoya kerrii · also called lucky heart, Valentine hoya · houseplant

Hoya kerrii is a slow-growing succulent vine from southeast Asia, famous for its heart-shaped leaves often sold as single-leaf cuttings. The leaf alone rarely produces stems; a cutting with a node will eventually trail. Pet-safe and undemanding once established.

A vining epiphyte found in mountainous jungle of Chiang Mai province, northern Thailand, where it climbs host trees; the thick heart-shaped leaf is a water-storing, semi-succulent adaptation to epiphytic life.

The popular single-leaf cutting almost never grows because it lacks a stem node: without a node it can root and survive for years but can never produce a vine, so a true plant needs a leaf with attached stem. Non-toxic to cats, dogs and horses per the ASPCA.

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

Watch for — Black spots on leaf: Edema from inconsistent watering or cold drafts.

Sources: aspca.org, en.wikipedia.org

What sweetheart plant's hardiness rating actually means

Sweetheart 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 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). Sweetheart plant has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

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

Sweetheart plant hardiness — frequently asked questions

Is sweetheart plant cold hardy?

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

What is the minimum temperature sweetheart plant can survive?

What hardiness zone is sweetheart plant?

Sweetheart plant is rated USDA 10-12 (indoor 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 sweetheart 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 sweetheart 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.