Cold hardiness & minimum temperature

Is Woolly Thyme (Thymus pseudolanuginosus)cold hardy? Hardiness zone & min temp

More about woolly thyme

About Woolly Thyme

Thymus pseudolanuginosus · herb

Woolly thyme is a flat, mat-forming groundcover thyme grown for its dense, silvery, fuzzy grey-green foliage rather than for cooking. It thrives in full sun and sharp drainage, tolerates foot traffic, and spreads to fill gaps between paving and rockery stones. It rarely flowers and dislikes wet, heavy soil.

Cold limit: USDA 4-9 (cold-hardy perennial groundcover) · RHS H5 (-12 to 27°C)

Watch for — Winter wet damage: In heavy, waterlogged winter soil the woolly foliage rots; plant in raised, gritty beds and avoid mulching directly over the crown.

What woolly thyme's hardiness rating actually means

Yes — woolly thyme is genuinely cold hardy. Rated RHS H5 and USDA 4-9 (cold-hardy perennial groundcover), 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 4-9 (cold-hardy perennial groundcover) — 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. Woolly Thyme is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for woolly thyme 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 woolly thyme go outside or overwinter — and where?

Plant it out within USDA 4-9 (cold-hardy perennial groundcover) 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 woolly thyme can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Woolly Thyme hardiness — frequently asked questions

Is woolly thyme cold hardy?

Yes — woolly thyme is genuinely cold hardy. Rated RHS H5 and USDA 4-9 (cold-hardy perennial groundcover), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Woolly Thyme is hardy across USDA 4-9 (cold-hardy perennial groundcover); 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 woolly thyme can survive?

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

What hardiness zone is woolly thyme?

Woolly Thyme is rated USDA 4-9 (cold-hardy perennial groundcover) and RHS H5 — Hardy in most of the UK and in cold winters.

Can woolly thyme survive winter outside?

Plant it out within USDA 4-9 (cold-hardy perennial groundcover) 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 woolly thyme 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.