Cold hardiness & minimum temperature

Is Silver Thyme (Thymus vulgaris 'Silver Posie')cold hardy? Hardiness zone & min temp

Also called silver thyme, variegated thyme.

More about silver thyme

About Silver Thyme

Thymus vulgaris 'Silver Posie' · also called silver thyme, variegated thyme · herb

Silver thyme is an ornamental, cream-and-grey variegated form of common thyme with the same warm, savoury flavour and pink-tinged new growth. A hardy, low, woody Mediterranean sub-shrub, it thrives in poor, sharply drained soil and full sun, shrugs off drought, and makes an evergreen edging or container herb that resents wet feet above all.

Cold limit: USDA 5-9 (hardy; the variegated form is slightly less robust in deep cold) · RHS H5 (10-24°C)

Watch for — Winter wet damage: More likely to die from cold, wet soil than from cold itself. Ensure sharp drainage and consider a gritty mulch or container that can be sheltered in a wet winter.

What silver thyme's hardiness rating actually means

Yes — silver thyme is genuinely cold hardy. Rated RHS H5 and USDA 5-9 (hardy; the variegated form is slightly less robust in deep cold), 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 (hardy; the variegated form is slightly less robust in deep cold) — 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. Silver Thyme is built for winter — once established it takes hard frost and snow in its stride.

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

Plant it out within USDA 5-9 (hardy; the variegated form is slightly less robust in deep cold) 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 silver thyme can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Silver Thyme hardiness — frequently asked questions

Is silver thyme cold hardy?

Yes — silver thyme is genuinely cold hardy. Rated RHS H5 and USDA 5-9 (hardy; the variegated form is slightly less robust in deep cold), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Silver Thyme is hardy across USDA 5-9 (hardy; the variegated form is slightly less robust in deep cold); 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 silver thyme can survive?

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

What hardiness zone is silver thyme?

Silver Thyme is rated USDA 5-9 (hardy; the variegated form is slightly less robust in deep cold) and RHS H5 — Hardy in most of the UK and in cold winters.

Can silver thyme survive winter outside?

Plant it out within USDA 5-9 (hardy; the variegated form is slightly less robust in deep cold) 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 silver 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.