Cold hardiness & minimum temperature

Is Spilanthes (Acmella oleracea)cold hardy? Hardiness zone & min temp

Also called Toothache Plant, Buzz Buttons, Paracress.

More about spilanthes

About Spilanthes

Acmella oleracea · also called Toothache Plant, Buzz Buttons · herb

Spilanthes, the toothache plant, is a low, spreading tender annual grown for its gold-and-red 'eyeball' flower buds and tingling, numbing leaves. Chewing a bud produces a buzzing, saliva-inducing sensation from spilanthol, used traditionally for oral pain. It loves heat, sun, and moist fertile soil, sprawling into a dense edible groundcover and flowering nonstop until frost.

Cold limit: USDA Grown as a warm-season annual; perennial only in frost-free zones 9-11 · RHS H1c (20-30°C)

Watch for — Frost sensitivity: As a tender tropical it is killed by the first frost. Grow as a summer annual, start under cover, and bring containers indoors or take cuttings before cold weather.

What spilanthes's hardiness rating actually means

Spilanthes 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 H1c means: Warm-temperate — can summer outdoors but must come in well before the first frost. On the US scale that maps to USDA Grown as a warm-season annual; perennial only in frost-free zones 9-11 — 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 5 °C (and never frost). Spilanthes has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for spilanthes as it gets too cold:

Below about about 5 °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 spilanthes go outside or overwinter — and where?

It can holiday outdoors in summer once nights are reliably above 5 °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 spilanthes can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1c figure above.

Spilanthes hardiness — frequently asked questions

Is spilanthes cold hardy?

Spilanthes 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. Spilanthes can only live outside year-round in genuinely frost-free climates (roughly USDA Grown as a warm-season annual; perennial only in frost-free zones 9-11); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature spilanthes can survive?

Minimum survivable temperature is roughly about 5 °C (and never frost). Spilanthes has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

What hardiness zone is spilanthes?

Spilanthes is rated USDA Grown as a warm-season annual; perennial only in frost-free zones 9-11 and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can spilanthes survive winter outside?

It can holiday outdoors in summer once nights are reliably above 5 °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 spilanthes below its minimum temperature?

Below about about 5 °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.