Cold hardiness & minimum temperature

Is Penny Mountain Thyme (Thymus pulegium)cold hardy? Hardiness zone & min temp

Also called Penny Mountain Thyme, Pennyroyal Thyme.

More about penny mountain thyme

About Penny Mountain Thyme

Thymus pulegium · also called Penny Mountain Thyme, Pennyroyal Thyme · herb

Penny Mountain Thyme is a low, mat-forming Mediterranean thyme species with small aromatic leaves and pale lilac flowers. It produces a sharp, pungent thyme-pennyroyal fragrance and is valued for ground cover, rock gardens, and herbal use. Drought-tolerant and fully sun-loving, it thrives in lean, well-drained soils and is reliably hardy in temperate gardens.

Cold limit: USDA 6–9 · RHS H5 (−10–30°C)

Watch for — Winter wet damage: In wet-winter climates, persistent moisture at the crown can kill established mats. Improve winter drainage, avoid mulching the crown, and ensure plants are in the most sun-exposed position.

What penny mountain thyme's hardiness rating actually means

Yes — penny mountain thyme is genuinely cold hardy. Rated RHS H5 and USDA 6–9, 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 6–9 — 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. Penny Mountain Thyme is built for winter — once established it takes hard frost and snow in its stride.

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

Plant it out within USDA 6–9 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 penny mountain thyme can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Penny Mountain Thyme hardiness — frequently asked questions

Is penny mountain thyme cold hardy?

Yes — penny mountain thyme is genuinely cold hardy. Rated RHS H5 and USDA 6–9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Penny Mountain Thyme is hardy across USDA 6–9; 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 penny mountain thyme can survive?

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

What hardiness zone is penny mountain thyme?

Penny Mountain Thyme is rated USDA 6–9 and RHS H5 — Hardy in most of the UK and in cold winters.

Can penny mountain thyme survive winter outside?

Plant it out within USDA 6–9 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 penny mountain 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.