Cold hardiness & minimum temperature

Is Thyme-leaved Sandwort (Arenaria serpyllifolia)cold hardy? Hardiness zone & min temp

Also called Thyme-leaved Sandwort, Thymeleaf Sandwort.

More about thyme-leaved sandwort

About Thyme-leaved Sandwort

Arenaria serpyllifolia · also called Thyme-leaved Sandwort, Thymeleaf Sandwort · flowering

Arenaria serpyllifolia is a delicate annual or biennial in the family Caryophyllaceae, native to dry, disturbed, and open habitats across Europe, Asia, and North Africa, and widely naturalised in North America. It produces tiny five-petalled white flowers from May to October on slender, much-branched stems clothed in small, ovate leaves that superficially resemble those of thyme. The most important care fact is excellent drainage: it thrives in gritty, infertile soils and is intolerant of waterlogged conditions. No toxicity to pets has been established for this species.

Cold limit: USDA 4-8 · RHS H5 (-15 to 30°C)

What thyme-leaved sandwort's hardiness rating actually means

Yes — thyme-leaved sandwort is genuinely cold hardy. Rated RHS H5 and USDA 4-8, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H5 means: Hardy in most of the UK and in cold 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 about −15 to −10 °C. Thyme-leaved Sandwort is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for thyme-leaved sandwort as it gets too cold:

It tolerates winter lows to about −15 to −10 °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 thyme-leaved sandwort 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 thyme-leaved sandwort can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Thyme-leaved Sandwort hardiness — frequently asked questions

Is thyme-leaved sandwort cold hardy?

Yes — thyme-leaved sandwort is genuinely cold hardy. Rated RHS H5 and USDA 4-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Thyme-leaved Sandwort 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 thyme-leaved sandwort can survive?

Minimum survivable temperature is roughly about −15 to −10 °C. Thyme-leaved Sandwort is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is thyme-leaved sandwort?

Thyme-leaved Sandwort is rated USDA 4-8 and RHS H5 — Hardy in most of the UK and in cold winters.

Can thyme-leaved sandwort 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 thyme-leaved sandwort below its minimum temperature?

It tolerates winter lows to about −15 to −10 °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.