One is the European pennyroyal (Mentha pulegium), which is a member of the mint family. The other is the American pennyroyal from an unrelated genus, Hedeoma pulegoides.
American Pennyroyal Plant
Either variety of pennyroyal has a fresh, minty scent but American pennyroyal is not in the mint family. They are both low growing plants with slightly hairy stems but the American has a square stem. It has many branches and creeps along at only 6 inches (15 cm.) to 1 foot (31 cm.) in height. The leaves are tiny and slim and the plant is rather unremarkable until bloom time in July. Until September the plant produces pale blue flower clusters that are dried and distilled for the oils.
European Pennyroyal Plant
True to its family nature, European pennyroyal has a spreading habit. The plants 1 foot (31 cm.) tall stems root wherever they touch the ground and start new plants. Care should be exercised when you grow pennyroyal plant and it may be best to plant in pots to minimize the invasiveness of the plant. European pennyroyal can be grown in full sun to partial shade in USDA zones 5 to 9. You can tell the difference between the two types of pennyroyal by the number of stamens. European has four but American flowers only have two.
How to Grow Pennyroyal Herb
Pennyroyal can be propagated from seed, cuttings, or spring division. The seed needs light to germinate but grows quickly once it sprouts. Plant them in prepared seed beds outside after all danger of frost. Sow the seed on the surface of the soil and mist the bed to moisten it. Keep it moist and germination should occur in two weeks. Divide established plants every three years in early spring for the best form and production. Pennyroyal is an easy to grow herb. European pennyroyal makes a wonderful trailing plant when grown in a hanging basket or at the edges of mixed color containers. American pennyroyal can be grown indoors in troughs or outside in the kitchen garden. Pinch the terminal ends of the herb to stimulate bushiness and a more compact growing shape. Grow pennyroyal as a groundcover in sunny areas with junky soil. The plant will persist even in unfavorable conditions and can be helpful in vegetation-free zones as an erosion control.
Cautions About Pennyroyal
Pennyroyal has been to relieve pain, gastrointestinal discomfort, soothe colds, and to aid in menstruation problems. The plant has also been used to induce abortion, so it should never be handled or ingested by a pregnant woman.
