Cold hardiness & minimum temperature

Is Boneset (Eupatorium perfoliatum)cold hardy? Hardiness zone & min temp

Also called boneset, thoroughwort, feverwort.

More about boneset

About Boneset

Eupatorium perfoliatum · also called boneset, thoroughwort · herb

Boneset (Eupatorium perfoliatum) is a North American wetland perennial recognised by its paired leaves fused around the hairy stem and flat clusters of fuzzy white flowers in late summer. It loves damp, sunny meadows and stream edges, draws masses of pollinators, and was a staple fever herb in folk medicine. It dies back to a tough crown each winter.

Cold limit: USDA 3-8 (cold-hardy outdoor perennial) · RHS H7 (-34 to 30°C)

What boneset's hardiness rating actually means

Yes — boneset is genuinely cold hardy. Rated RHS H7 and USDA 3-8 (cold-hardy outdoor perennial), 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 3-8 (cold-hardy outdoor perennial) — 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. Boneset is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for boneset 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 boneset go outside or overwinter — and where?

Plant it out within USDA 3-8 (cold-hardy outdoor perennial) 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 boneset can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Boneset hardiness — frequently asked questions

Is boneset cold hardy?

Yes — boneset is genuinely cold hardy. Rated RHS H7 and USDA 3-8 (cold-hardy outdoor perennial), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Boneset is hardy across USDA 3-8 (cold-hardy outdoor perennial); 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 boneset can survive?

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

What hardiness zone is boneset?

Boneset is rated USDA 3-8 (cold-hardy outdoor perennial) and RHS H7 — Hardy in the severest European continental winters.

Can boneset survive winter outside?

Plant it out within USDA 3-8 (cold-hardy outdoor perennial) 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 boneset 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.