Cold hardiness & minimum temperature

Is Cushion Sandwort (Arenaria tetraquetra)cold hardy? Hardiness zone & min temp

Also called Cushion Sandwort, Four-sided Sandwort.

More about cushion sandwort

About Cushion Sandwort

Arenaria tetraquetra · also called Cushion Sandwort, Four-sided Sandwort · flowering

Cushion Sandwort is a tight cushion-forming alpine perennial native to the mountains of Spain and southern France. It produces tiny white flowers in late spring above dense, compact mounds of overlapping leaves. A classic choice for alpine troughs, scree gardens, and rock crevices; demands perfect drainage and full sun to thrive.

Cold limit: USDA 4-7 · RHS H7 (-25°C to 20°C)

Watch for — Cushion rot: Moisture trapped in the tight cushion in winter or humid summers causes interior rot. Improve drainage drastically, consider alpine house protection in winter, and ensure excellent air circulation.

What cushion sandwort's hardiness rating actually means

Yes — cushion sandwort is genuinely cold hardy. Rated RHS H7 and USDA 4-7, 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 4-7 — 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. Cushion Sandwort is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for cushion sandwort 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 cushion sandwort go outside or overwinter — and where?

Plant it out within USDA 4-7 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 cushion sandwort can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Cushion Sandwort hardiness — frequently asked questions

Is cushion sandwort cold hardy?

Yes — cushion sandwort is genuinely cold hardy. Rated RHS H7 and USDA 4-7, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Cushion Sandwort is hardy across USDA 4-7; 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 cushion sandwort can survive?

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

What hardiness zone is cushion sandwort?

Cushion Sandwort is rated USDA 4-7 and RHS H7 — Hardy in the severest European continental winters.

Can cushion sandwort survive winter outside?

Plant it out within USDA 4-7 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 cushion sandwort 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.