Cold hardiness & minimum temperature

Is bluejoint reedgrass (Calamagrostis canadensis)cold hardy? Hardiness zone & min temp

Also called bluejoint reedgrass, bluejoint, Canadian reedgrass.

More about bluejoint reedgrass

About bluejoint reedgrass

Calamagrostis canadensis · also called bluejoint reedgrass, bluejoint · flowering

Bluejoint reedgrass is a vigorous native North American cool-season grass thriving in wet meadows, marshes, and streambanks. It forms dense stands of upright, arching stems topped with purple-tinged panicles in early summer that fade to tawny gold. Excellent for naturalising wet and boggy areas, it provides important wildlife and waterfowl habitat and erosion control along watercourses.

Cold limit: USDA 3-9 · RHS H7 (-34 to 28°C)

Watch for — Summer decline: As a cool-season grass it may look tired in hot, humid summers; keep moisture levels high and it will recover with autumn's cooler temperatures.

What bluejoint reedgrass's hardiness rating actually means

Yes — bluejoint reedgrass is genuinely cold hardy. Rated RHS H7 and USDA 3-9, 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 3-9 — 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. bluejoint reedgrass is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for bluejoint reedgrass 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 bluejoint reedgrass go outside or overwinter — and where?

Plant it out within USDA 3-9 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 bluejoint reedgrass can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

bluejoint reedgrass hardiness — frequently asked questions

Is bluejoint reedgrass cold hardy?

Yes — bluejoint reedgrass is genuinely cold hardy. Rated RHS H7 and USDA 3-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. bluejoint reedgrass is hardy across USDA 3-9; 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 bluejoint reedgrass can survive?

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

What hardiness zone is bluejoint reedgrass?

bluejoint reedgrass is rated USDA 3-9 and RHS H7 — Hardy in the severest European continental winters.

Can bluejoint reedgrass survive winter outside?

Plant it out within USDA 3-9 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 bluejoint reedgrass 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.