Cold hardiness & minimum temperature

Is autumn red grass (Miscanthus oligostachyus 'Purpurascens')cold hardy? Hardiness zone & min temp

Also called autumn red grass, flame grass, purple autumn grass.

More about autumn red grass

About autumn red grass

Miscanthus oligostachyus 'Purpurascens' · also called autumn red grass, flame grass · flowering

Miscanthus oligostachyus 'Purpurascens' — commonly called flame grass — is one of the earliest Miscanthus to turn colour, with mid-green foliage igniting brilliant orange-red from midsummer onward. Silvery-white plumes appear in late summer. More compact than many Miscanthus sinensis cultivars and exceptionally cold-hardy, it suits smaller gardens and northern climates.

Cold limit: USDA 4–9 · RHS H7 (-30°C to 35°C)

Watch for — Crown heave in freeze-thaw cycles: In very cold, poorly drained sites, repeated freezing and thawing can heave the crown. Plant in well-drained soil; mulch around (not over) the crown in autumn in zones 4–5.

What autumn red grass's hardiness rating actually means

Yes — autumn red grass is genuinely cold hardy. Rated RHS H7 and USDA 4–9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H7 means: Hardy in the severest European continental winters. On the US scale that maps to USDA 4–9 — 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 below about −20 °C. autumn red grass is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for autumn red grass as it gets too cold:

It tolerates winter lows to about −20 °C once established.
Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root.
First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.

Can autumn red grass go outside or overwinter — and where?

Plant it out within USDA 4–9 and it overwinters with little or no help.
It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy.
The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

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 autumn red grass can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

autumn red grass hardiness — frequently asked questions

Is autumn red grass cold hardy?

Yes — autumn red grass is genuinely cold hardy. Rated RHS H7 and USDA 4–9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. autumn red grass is hardy across USDA 4–9; it belongs in the ground or a frost-proof container, not on a windowsill, and many types actively need a cold winter to perform.

What is the minimum temperature autumn red grass can survive?

Minimum survivable temperature is roughly below about −20 °C. autumn red grass is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is autumn red grass?

autumn red grass is rated USDA 4–9 and RHS H7 — Hardy in the severest European continental winters.

Can autumn red grass survive winter outside?

Plant it out within USDA 4–9 and it overwinters with little or no help. It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy. The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

What happens to autumn red grass below its minimum temperature?

It tolerates winter lows to about −20 °C once established. Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root. First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.