Cold hardiness & minimum temperature

Is Purple Moor Grass (Molinia caerulea 'Moorhexe')cold hardy? Hardiness zone & min temp

Also called purple moor grass, moor grass, Moorhexe moor grass.

More about purple moor grass

About Purple Moor Grass

Molinia caerulea 'Moorhexe' · also called purple moor grass, moor grass · flowering

Molinia caerulea 'Moorhexe' is a compact, upright deciduous grass prized for its narrow, tufted habit and rich purple-tinged flower spikes in late summer. It thrives in moist, acidic soils and is exceptionally well suited to rain gardens, bog edges, and naturalistic plantings. Autumn colour turns golden-yellow before the foliage collapses cleanly to the ground.

Cold limit: USDA 4-9 · RHS H7 (-20°C to 30°C)

What purple moor grass's hardiness rating actually means

Yes — purple moor 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. Purple Moor Grass is built for winter — once established it takes hard frost and snow in its stride.

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

Purple Moor Grass hardiness — frequently asked questions

Is purple moor grass cold hardy?

Yes — purple moor 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. Purple Moor 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 purple moor grass can survive?

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

What hardiness zone is purple moor grass?

Purple Moor Grass is rated USDA 4-9 and RHS H7 — Hardy in the severest European continental winters.

Can purple moor 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 purple moor 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.