Cold hardiness & minimum temperature

Is Brunnera macrophylla 'Jack Frost' (Brunnera macrophylla 'Jack Frost')cold hardy? Hardiness zone & min temp

Also called Jack Frost Siberian bugloss, Jack Frost brunnera.

More about brunnera macrophylla 'jack frost'

About Brunnera macrophylla 'Jack Frost'

Brunnera macrophylla 'Jack Frost' · also called Jack Frost Siberian bugloss, Jack Frost brunnera · flowering

An award-winning shade perennial grown for its frosted, silver-overlaid heart-shaped leaves traced with green veins and margins. In mid to late spring it throws up airy sprays of tiny sky-blue, forget-me-not flowers. A clump-forming, low-maintenance groundcover for moist woodland shade, lighting up dark corners all season with metallic foliage.

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

Watch for — Loss of silver frosting: In deep shade or poor light the metallic effect can dull. Bright, indirect woodland light keeps the frosting at its best without scorching.

What brunnera macrophylla 'jack frost''s hardiness rating actually means

Yes — brunnera macrophylla 'jack frost' 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 'Jack Frost' is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for brunnera macrophylla 'jack frost' 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 'jack frost' 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 'jack frost' 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 'Jack Frost' hardiness — frequently asked questions

Is brunnera macrophylla 'jack frost' cold hardy?

Yes — brunnera macrophylla 'jack frost' 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 'Jack Frost' 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 'jack frost' can survive?

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

What hardiness zone is brunnera macrophylla 'jack frost'?

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

Can brunnera macrophylla 'jack frost' 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 'jack frost' 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.