Cold hardiness & minimum temperature

Is Rock Cress (Aubrieta deltoidea)cold hardy? Hardiness zone & min temp

Also called Rock Cress, Aubrieta, Purple Rock Cress.

More about rock cress

About Rock Cress

Aubrieta deltoidea · also called Rock Cress, Aubrieta · flowering

A vigorous, mat-forming perennial producing masses of small cross-shaped flowers in shades of purple, lilac, mauve, and pink in spring. Native to stony habitats from south-eastern Europe to western Asia. Widely grown to cascade over walls, rock gardens, and raised beds. Thrives in poor, alkaline soils with full sun and sharp drainage.

Cold limit: USDA 4–8 · RHS H7 (-20 to 25°C)

What rock cress's hardiness rating actually means

Yes — rock cress is genuinely cold hardy. Rated RHS H7 and USDA 4–8, 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 4–8 — 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. Rock Cress is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for rock cress 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 rock cress go outside or overwinter — and where?

Plant it out within USDA 4–8 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 rock cress can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Rock Cress hardiness — frequently asked questions

Is rock cress cold hardy?

Yes — rock cress is genuinely cold hardy. Rated RHS H7 and USDA 4–8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Rock Cress is hardy across USDA 4–8; 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 rock cress can survive?

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

What hardiness zone is rock cress?

Rock Cress is rated USDA 4–8 and RHS H7 — Hardy in the severest European continental winters.

Can rock cress survive winter outside?

Plant it out within USDA 4–8 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 rock cress 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.