Pennyroyal
Mentha pulegium
Pennyroyal is a low, creeping mint with a sharp, spearmint-like aroma traditionally used as an insect repellent. Despite its history, its concentrated oil is highly toxic and it should never be taken internally.
- Light
- Full sun to part shade
- Water
- Regular; likes moist soil
- Difficulty
- Easy
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Overview
Pennyroyal (Mentha pulegium) is a low, mat-forming perennial in the mint family (Lamiaceae), native to Europe, North Africa and western Asia.
It has a powerful, sharp minty scent and a long history as a strewing herb and insect repellent, especially against fleas and mosquitoes — its species name pulegium derives from the Latin for flea.
Important safety note: while historically used in folk medicine, pennyroyal contains pulegone, and its concentrated essential oil is highly toxic to the liver and has caused serious poisoning and deaths. It must never be ingested, and is especially dangerous during pregnancy. Today it is grown mainly as a ground cover and aromatic repellent.
How to identify it
- Leaves: small, oval, grey-green, in opposite pairs, releasing a strong spearmint-like aroma when crushed
- Flowers: small lilac to pale purple flowers in tight whorls clustered around the stem at the leaf joints, in summer
- Stems: square (typical of mints), creeping and rooting at the nodes, then turning upward; mat-forming, usually under 30 cm
- Habit: low, spreading ground-hugging perennial
- Scent: sharp, penetrating mint fragrance
Care & growing
Light: Full sun to partial shade.
Water: Likes consistently moist soil; reflects its damp natural habitat.
Soil: Moist, fertile soil; tolerates a range of conditions.
Temperature: Hardy through about USDA zones 6-9.
Feeding: Minimal; like most mints it grows readily.
Propagation: Very easy from division, stem cuttings or rooted runners; it spreads quickly and can become invasive, so contain it. Handle and grow it only as an ornamental/repellent, never for consumption.
Habitat & origin
Pennyroyal is native to Europe, North Africa and western Asia, where it grows in damp meadows, the muddy margins of ponds and streams, and seasonally wet ground.
It has naturalized in parts of North America and elsewhere and is considered invasive in some regions. In gardens it is grown as a fragrant creeping ground cover and around seating areas as an insect deterrent.
Uses & benefits
Insect repellent: Historically valued to repel fleas and mosquitoes; crushed foliage and dried plants were strewn or placed near bedding and pets.
Ornamental: A low, aromatic ground cover that releases scent when brushed or walked on.
Ecological: The flowers attract bees and other pollinators.
Warning: Despite folk-medicine history, pennyroyal and especially its essential oil are toxic and can be fatal; it should not be consumed and is hazardous in pregnancy.
Frequently asked questions
Is pennyroyal safe to use?
It is safe to grow as an ornamental and aromatic repellent, but it should never be taken internally. Its essential oil contains pulegone, which is highly toxic to the liver and has caused fatal poisonings.
Why is pennyroyal used against insects?
Its strong minty oils repel fleas and mosquitoes, and it was traditionally strewn or placed near pets and bedding for this purpose; the name pulegium comes from the Latin for flea.
Is pennyroyal dangerous during pregnancy?
Yes, extremely. Pennyroyal, especially its oil, has been used historically to induce abortion and has caused severe poisoning and death; it must be avoided entirely in pregnancy.
Does pennyroyal spread aggressively?
Yes. Like other mints it creeps and roots at the nodes, spreading quickly, and is considered invasive in some areas, so it is best contained.
Pennyroyal guides
In-depth guides for identifying, growing, and caring for Pennyroyal.
