Cold hardiness & minimum temperature

Is Globe amaranth (Gomphrena globosa)cold hardy? Hardiness zone & min temp

Also called Globe amaranth, bachelor's button, makhmali.

More about globe amaranth

About Globe amaranth

Gomphrena globosa · also called Globe amaranth, bachelor's button · flowering

Globe amaranth is a heat-loving tropical annual producing clover-like, papery flowerheads in vibrant shades of magenta, purple, pink, white, and red from summer until frost. Native to Central America, it thrives in full sun and dry to moderately moist conditions. An exceptional cut and dried flower, it is widely grown in US gardens for its long bloom season.

Cold limit: USDA 2-11 (annual) · RHS H1c (18–38°C)

Watch for — Slow establishment in cool springs: Seeds and transplants stall in soil below 18°C. Do not direct-sow outdoors until soil has warmed; start indoors 4–6 weeks before the last frost date. Transplants set out too early will sit dormant and may rot.

What globe amaranth's hardiness rating actually means

Globe amaranth 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 2-11 (annual) — 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). Globe amaranth has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for globe amaranth 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 globe amaranth 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 globe amaranth can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1c figure above.

Globe amaranth hardiness — frequently asked questions

Is globe amaranth cold hardy?

Globe amaranth 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. Globe amaranth can only live outside year-round in genuinely frost-free climates (roughly USDA 2-11 (annual)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature globe amaranth can survive?

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

What hardiness zone is globe amaranth?

Globe amaranth is rated USDA 2-11 (annual) and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can globe amaranth 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 globe amaranth 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.