Cold hardiness & minimum temperature

Is Hairy Rock-cress (Arabis hirsuta)cold hardy? Hardiness zone & min temp

Also called Hairy Rock-cress, Hairy Rockcress, Mountain Rockcress.

More about hairy rock-cress

About Hairy Rock-cress

Arabis hirsuta · also called Hairy Rock-cress, Hairy Rockcress · flowering

Arabis hirsuta is a small biennial or short-lived perennial in the Brassicaceae family, native to calcareous grasslands, rocky outcrops, walls, and limestone pavements across Europe and North America. It forms a rosette of hairy, oblong leaves from which erect flowering stems carry small four-petalled white flowers from May to August. The most important care fact is that it is strictly a calcicole — it grows on base-rich, well-drained, alkaline or neutral substrates and will not persist on acid soils. No significant toxicity to pets has been reported.

Cold limit: USDA 4-8 · RHS H6 (-20 to 25°C)

Watch for — Crown rot in wet or heavy soils: Persistent moisture around the hairy basal rosette, especially in winter, leads to fungal rotting of the crown; plant in raised beds or rock gardens with gritty, free-draining compost to prevent this.

What hairy rock-cress's hardiness rating actually means

Yes — hairy rock-cress is genuinely cold hardy. Rated RHS H6 and USDA 4-8, 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 4-8 — 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 about −20 to −15 °C. Hairy Rock-cress is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for hairy rock-cress 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 hairy 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 hairy rock-cress can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Hairy Rock-cress hardiness — frequently asked questions

Is hairy rock-cress cold hardy?

Yes — hairy rock-cress is genuinely cold hardy. Rated RHS H6 and USDA 4-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Hairy 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 hairy rock-cress can survive?

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

What hardiness zone is hairy rock-cress?

Hairy Rock-cress is rated USDA 4-8 and RHS H6 — Hardy throughout the UK and northern Europe.

Can hairy 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 hairy rock-cress 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.