Cold hardiness & minimum temperature

Is Pennyroyal (Mentha pulegium)cold hardy? Hardiness zone & min temp

Also called European Pennyroyal.

More about pennyroyal

About Pennyroyal

Mentha pulegium · also called European Pennyroyal · herb

Pennyroyal is a low, spreading mint with a sharp, almost acrid peppermint scent, historically used as an insect repellent but NOT a culinary herb — it is toxic to people and pets. A hardy creeping perennial, it likes moist soil and sun to part shade, but its pulegone-rich oil makes it dangerous to ingest, especially for cats.

Cold limit: USDA 6-9 (perennial outdoors; dies back in winter) · RHS H5 (15-24°C)

Watch for — Winter loss in cold zones: Less hardy than common mint and can perish in cold, wet winters. Mulch the crown or overwinter divisions under cover.

What pennyroyal's hardiness rating actually means

Yes — pennyroyal is genuinely cold hardy. Rated RHS H5 and USDA 6-9 (perennial outdoors; dies back in winter), 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 (perennial outdoors; dies back in winter) — 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. Pennyroyal is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for pennyroyal 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 pennyroyal go outside or overwinter — and where?

Plant it out within USDA 6-9 (perennial outdoors; dies back in winter) 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 pennyroyal can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Pennyroyal hardiness — frequently asked questions

Is pennyroyal cold hardy?

Yes — pennyroyal is genuinely cold hardy. Rated RHS H5 and USDA 6-9 (perennial outdoors; dies back in winter), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Pennyroyal is hardy across USDA 6-9 (perennial outdoors; dies back in winter); 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 pennyroyal can survive?

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

What hardiness zone is pennyroyal?

Pennyroyal is rated USDA 6-9 (perennial outdoors; dies back in winter) and RHS H5 — Hardy in most of the UK and in cold winters.

Can pennyroyal survive winter outside?

Plant it out within USDA 6-9 (perennial outdoors; dies back in winter) 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 pennyroyal 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.