Cold hardiness & minimum temperature

Is Mountain Lemon Thyme (Thymus nervosus)cold hardy? Hardiness zone & min temp

Also called Mountain lemon thyme, Pyrenean thyme.

More about mountain lemon thyme

About Mountain Lemon Thyme

Thymus nervosus · also called Mountain lemon thyme, Pyrenean thyme · herb

Thymus nervosus is an aromatic, compact sub-shrub native to mountain grasslands and rocky slopes of the Pyrenees and Cantabrian Mountains, typically at subalpine elevations. It produces small, bright pink-purple flowers in summer and carries a distinctly lemony fragrance similar to Thymus citriodorus, making it attractive for both alpine planting and herb gardens. Like all thymes, sharp drainage and a sunny, open position are essential — winter wet is far more damaging than cold. The ASPCA classifies thyme as non-toxic to cats, dogs, and horses.

Cold limit: USDA 5-9 · RHS H5 (-20 to 28°C)

Watch for — Winter crown rot: High rainfall combined with poor drainage causes the crown and lower stems to rot over winter. A grit collar around the base and a south-facing aspect are the most effective preventive measures.

What mountain lemon thyme's hardiness rating actually means

Yes — mountain lemon thyme is genuinely cold hardy. Rated RHS H5 and USDA 5-9, 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 5-9 — 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. Mountain Lemon Thyme is built for winter — once established it takes hard frost and snow in its stride.

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

Plant it out within USDA 5-9 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 mountain lemon thyme can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Mountain Lemon Thyme hardiness — frequently asked questions

Is mountain lemon thyme cold hardy?

Yes — mountain lemon thyme is genuinely cold hardy. Rated RHS H5 and USDA 5-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Mountain Lemon Thyme is hardy across USDA 5-9; 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 mountain lemon thyme can survive?

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

What hardiness zone is mountain lemon thyme?

Mountain Lemon Thyme is rated USDA 5-9 and RHS H5 — Hardy in most of the UK and in cold winters.

Can mountain lemon thyme survive winter outside?

Plant it out within USDA 5-9 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 mountain lemon 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.