Cold hardiness & minimum temperature

Is Red amaranth (Amaranthus cruentus)cold hardy? Hardiness zone & min temp

Also called Red amaranth, Purple amaranth, Blood amaranth, African spinach.

More about red amaranth

About Red amaranth

Amaranthus cruentus · also called Red amaranth, Purple amaranth · flowering

Red amaranth is a vigorous, heat-loving annual grown for both its dramatic plum-red or crimson flower plumes and its highly nutritious edible leaves and seeds. Tolerant of drought and poor soil, it performs best in full sun with moderate fertility. Its architectural stature makes it a striking border plant and excellent dried flower.

Cold limit: USDA 2–11 (grown as annual) · RHS H1c (18–35°C)

Watch for — Damping-off in seedlings: Young seedlings collapse at soil level in cold, wet, or poorly ventilated conditions. Sow in warm (21°C+) well-drained compost. Avoid overwatering and provide good air circulation during germination.

What red amaranth's hardiness rating actually means

Red 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 (grown as 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). Red amaranth has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

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

Red amaranth hardiness — frequently asked questions

Is red amaranth cold hardy?

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

What is the minimum temperature red amaranth can survive?

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

What hardiness zone is red amaranth?

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

Can red 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 red 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.