Cold hardiness & minimum temperature

Is Large Masterwort (Astrantia maxima)cold hardy? Hardiness zone & min temp

Also called Greater Masterwort, Maxima Masterwort.

More about large masterwort

About Large Masterwort

Astrantia maxima · also called Greater Masterwort, Maxima Masterwort · flowering

Large Masterwort is a robust herbaceous perennial native to the Caucasus, bearing larger-than-average pink pincushion flower heads surrounded by prominent spreading bracts from early to mid-summer. Larger than Astrantia major, it suits shaded woodland gardens and moist borders. Treat as mildly toxic around pets.

Cold limit: USDA 4-9 · RHS H6 (-20-25°C)

What large masterwort's hardiness rating actually means

Yes — large masterwort is genuinely cold hardy. Rated RHS H6 and USDA 4-9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H6 means: Hardy throughout the UK and northern Europe. 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 about −20 to −15 °C. Large Masterwort is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for large masterwort as it gets too cold:

It tolerates winter lows to about −20 to −15 °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 large masterwort 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 large masterwort can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Large Masterwort hardiness — frequently asked questions

Is large masterwort cold hardy?

Yes — large masterwort is genuinely cold hardy. Rated RHS H6 and USDA 4-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Large Masterwort 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 large masterwort can survive?

Minimum survivable temperature is roughly about −20 to −15 °C. Large Masterwort is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is large masterwort?

Large Masterwort is rated USDA 4-9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can large masterwort 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 large masterwort below its minimum temperature?

It tolerates winter lows to about −20 to −15 °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.