Mentha pulegium - Pennyroyal, Pond Marginal Plant

Mentha pulegium, known as pennyroyal, is a scarce UK native mint that forms a low, creeping mat of small, strongly mint-scented leaves. In summer it carries whorls of lilac to pale lavender-pink flowers. In the wild it grows in seasonally flooded grassland and around pools.

Pennyroyal at a glance

Botanical name	Mentha pulegium
Common name	Pennyroyal
Plant type	Low, creeping, mat-forming perennial; dies back in winter
Height and spread	Low mat; flower stems about 10–50 cm (sources differ), spreading 10–50 cm
Flowers	Lilac to pale lavender-pink, in whorls, June to September
Position	Full sun or part shade
Soil	Moist or wet soil; any pH; chalk, clay, loam or sand
Pond depth	0–1 cm – wet soil or the very shallow edge
Hardiness	RHS H7 – very hardy (below -20°C)
Native to	UK (scarce native wild flower)

Is pennyroyal poisonous?

Yes. Although it is a mint, it is not a culinary herb. The RHS says it is harmful if eaten and not edible. It contains pulegone, which damages the liver, and people have been poisoned after mistaking it for culinary mint. It should not be used in pregnancy, and it is toxic to cats. Wear gloves when handling it and keep pets away from it.

Is it legal to grow?

Yes, as nursery-grown stock. Wild pennyroyal is endangered in Great Britain and protected under Schedule 8 of the Wildlife and Countryside Act, so never collect it from the wild.

Where to plant pennyroyal

Wet soil or the very shallow edge of a wildlife pond
Damp ground that floods in winter
Full sun or part shade, away from pets

How to plant and care for it

Plant in spring in moist or wet soil. The RHS warns it may become a nuisance if not managed, so trim back wandering stems. Bees visit the flowers. Watch for mint rust and powdery mildew.

Which size should I buy?

Bare-root plants (7 cm, 9 cm, 1 litre and 3 litre) arrive without a pot or compost and are the most economical way to plant a group. Potted plants (9 cm, 1 litre and 3 litre) arrive growing in our peat-free compost and give a faster display. Packs of 3 come in 7 cm, 9 cm, 1 litre and 3 litre bare-root sizes and cost less per plant. The 2x Pot & Compost option is two plants supplied with pots and compost.