Cold hardiness & minimum temperature

Is Brunnera macrophylla 'Looking Glass' (Brunnera macrophylla 'Looking Glass')cold hardy? Hardiness zone & min temp

Also called Looking Glass brunnera.

More about brunnera macrophylla 'looking glass'

About Brunnera macrophylla 'Looking Glass'

Brunnera macrophylla 'Looking Glass' · also called Looking Glass brunnera · flowering

A dazzling sport of 'Jack Frost' with almost entirely silver, metallic heart-shaped leaves showing only faint green veining. Sprays of sky-blue forget-me-not flowers rise above the shimmering foliage in spring. This clump-forming shade perennial brightens dark woodland corners like a mirror, but its near-white leaves are more prone to sun scorch than greener types.

Cold limit: USDA 3-8 · RHS H7 (-1 to 24°C active growth (hardy to about -40°C dormant))

Watch for — Crown rot: Waterlogged soil rots the crown over winter. Plant in free-draining, humus-rich ground.

What brunnera macrophylla 'looking glass''s hardiness rating actually means

Yes — brunnera macrophylla 'looking glass' is genuinely cold hardy. Rated RHS H7 and USDA 3-8, 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 — 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. Brunnera macrophylla 'Looking Glass' is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for brunnera macrophylla 'looking glass' 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 brunnera macrophylla 'looking glass' go outside or overwinter — and where?

Plant it out within USDA 3-8 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 brunnera macrophylla 'looking glass' can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Brunnera macrophylla 'Looking Glass' hardiness — frequently asked questions

Is brunnera macrophylla 'looking glass' cold hardy?

Yes — brunnera macrophylla 'looking glass' is genuinely cold hardy. Rated RHS H7 and USDA 3-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Brunnera macrophylla 'Looking Glass' is hardy across USDA 3-8; 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 brunnera macrophylla 'looking glass' can survive?

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

What hardiness zone is brunnera macrophylla 'looking glass'?

Brunnera macrophylla 'Looking Glass' is rated USDA 3-8 and RHS H7 — Hardy in the severest European continental winters.

Can brunnera macrophylla 'looking glass' survive winter outside?

Plant it out within USDA 3-8 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 brunnera macrophylla 'looking glass' 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.