Growing Pennyroyal: How To Grow Pennyroyal Herb

By: Bonnie L. Grant, Certified Urban Agriculturist

Pennyroyal plant is a perennial herb that was once widely used but is not as common today. It has applications as an herbal remedy, culinary uses and as a decorative touch. Growing pennyroyal in the herb or perennial garden will add color with its reddish purple to lilac blooms. There are two plants called pennyroyal.

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 is many branched and creeps along at only 6 inches (15 cm.) to 1 foot (30 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 (30 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 ground cover 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.

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Pennyroyal Plant - Tips For Growing Pennyroyal - garden

Family: Lamiaceae (Labiatae), Hedeoma pulegioides (L.) Pers. and Mentha pulegium L.

Source : Simon, J.E., A.F. Chadwick and L.E. Craker. 1984. Herbs: An Indexed Bibliography. 1971-1980. The Scientific Literature on Selected Herbs, and Aromatic and Medicinal Plants of the Temperate Zone. Archon Books, 770 pp., Hamden, CT.

Pennyroyal represents plants of two genera, Mentha pulegium L., European pennyroyal, and Hedeoma pulegioides (L.) Pers., American pennyroyal. European pennyroyal is a low, prostrate, and spreading perennial herb, native to Europe and western Asia. Reaching a height of 0.3 meters, the plant has ovate to nearly orbicular leaves and lilac flowers. American pennyroyal is a low-growing annual plant, native to the eastern part of the United States. Reaching a height of 0.3 meters, the plant has multibranched pubescent stems, small, narrow, elliptic leaves, and light blue to purple flowers that appear in the summer months.

The reported life zone of European pennyroyal is 7 to 26 degrees centigrade with an annual precipitation of 0.3 to 1.2 meters and a soil pH of 4.8 to 8.3 (4.1-31). The plant is found in humid, low-coastal regions along the Mediterranean Sea, and grows best in fertile, moist soils with partial shade (14.1-8). American pennyroyal grows on dry, sandy soils and is commercially cultivated to only a very limited extent.

The essential oil of pennyroyal is obtained by steam distillation from leaves and flowering tops. The oil consists chiefly of pulegone but also contains menthone, isomenthone, l--pinene, l-limonene, dipentene, menthol, and other compounds (14.1-35). American pennyroyal has a similar essential oil. Other chemical constituents include bitter principle and tannin (14.1-35).

The leaves of pennyroyal have a strong mint-like odor and are used fresh or dried in culinary preparations, especially puddings from which it derives the name 'pudding grass.' The essential oil is used as a fragrance in cosmetics. Pulegone from the essential oil is used as a starting material for the manufacture of synthetic menthol.

As a medicinal plant, pennyroyal has traditionally been used as an antispasmodic, carminative, diaphoretic, emmenagogue, sedative, stimulant, aromatic, and stomachic. It has been used to promote menstruation, induce abortion, cure headaches, and relieve colds (11.1-101). The essential oil can be toxic, causing nausea, vomiting, diarrhea, depression, stimulation, and convulsions (8.2-19, 11.1-136). Pennyroyal is pharmaceutically classified as a diaphoretic and emmenagogue (14.1-35). The plant has been used as an insect repellent against fleas and other pests. Plants and oil can cause contact dermatitis (11.1-96).

European and American pennyroyal are generally recognized as safe for human consumption (21 CFR section 172.50 [l982]).

[Note: References listed above in parentheses can be found in full in the original reference].
Aromatic and Medicinal Plants Index

Photo: Penny Woodward

The hot dry weather brings out all manner of insects, but the most problematic at present are the ants. When we lived in an area with sandy soils they were a constant problem coming in to the kitchen and bathrooms looking for moisture. In our current house we are surrounded by heavier clay soils and ants haven't been a problem inside, but I have had some issues with them in pots outside. I dunk the smaller pots in soapy water and then rinse through well with fresh water. The ants exit pretty quickly. But my lime in a half wine barrel is a bit too big to move, so instead I planted pennyroyal around the outside. It took twelve months but the ants that had been nesting in the soil, in the base of the pot, disappeared.

Pennyroyal (Mentha pulegium) has leaves that are slightly hairy and narrowly elliptic, while the mauve (or sometimes white) flowers grow in tiers of whorled clusters. Sometimes called fleabane, it has a camphor/peppermint scent and does best in moist, humus-rich soils in semi-shade. Grow new plants from seed or by root division in spring and summer. It spreads rapidly from underground runners and can be a problem invading river banks and other damp areas. So don’t grow it if you live near these sorts of bush regions.

There is also a native pennyroyal (M. satureioides) that has similar properties. It grows to about 30cm, with a creeping habit and opposite green leaves that taper at both ends. The flowers are white and occur in spring. This pennyroyal will grow in dry and damp places and is found Australia-wide. The whole plant has a strong mint smell and the leaves contain oil rich in pulegone, the same oil that is found in M. pulegium. Pennyroyals act by deterring insects from feeding and can be strewn on benches or shelves to repel ants or grown near the point where they enter the house. Pennyroyals are also good mosquito and flea repellents for people and pets—grow them near dog kennels and in damp corners of the garden where mosquitoes may breed.

When I’m working in the garden, if mosquitoes are a problem, I grab a few leaves and rub them on any exposed bits of skin. This will also keep flies away for short periods.

SERIES 31 | Episode 15

Jerry takes a close look at the Native Pennyroyal and explains why it is one of his favourite native herbs.

COMMON NAME Native Pennyroyal, Creeping Mint
BOTANICAL NAME Mentha satureioides
ORIGIN Australia
HABIT Clumping perennial groundcover herb around 20cm high with 40cm spread
FEATURES Small white flowers attract bees
USES Leaves have a delicate mint flavour that can be used in cooking. Great in pots or in the garden
BEST CLIMATE/POSITION Light shade to full sun
CARE Protect from frosts. If grown in sandy soils, make sure to water
PROPAGATION By seed, cuttings or divisions
POTENTIAL PROBLEMS Can spread, so best grown in pots to prevent escaping

One of Jerry’s favourite native herbs is native pennyroyal, Mentha satureioides.

It's a delicately flavoured mint that you can use in cooking without it dominating the dish.

In drought, it will die right back down to the ground, so for a year-round harvest, Jerry stand his wide pot of pennyroyal in a dish of water.

It is vigorous, so growing it in a pot restricts its ability to spread.

Every year, Jerry splits up his plant into four equal portions, repotting one portion, which will refill the pot within six months. If you don't do that, then plants tend to wither away.

Native pennyroyal is usually sold by native specialists, and community nurseries.

In the wild, it grows anywhere from Townsville down to Melbourne and across to Adelaide, so it adapts readily to many climates.

As far back as 1768 the phrase “a pretty penny” meant a lot of money. As of 2013, it now costs the U.S. Mint 1.83 cents to mint and distribute each new penny. In 1792 things were quite different, and was a pennyworth so much that we had halfpenny coins. The Treasury wanted to mint pennies containing a penny’s worth of copper. That way it wouldn’t pay to counterfeit coins if you had to use a penny’s worth of copper to make a penny coin.

Putting a penny’s worth of copper into a coin would make the pennies huge, even larger than a half dollar.

So they made small pennies with a silver plug in the middle. The silver plus the copper added up to just about a penny’s worth of metal. The Silver Center Cent was the very first coin minted at the new Philadelphia Mint building in 1792.

Superb metallurgy wasn’t the only skill that Colonial Americans had. They learned to use plants of the woods and herbs brought from other lands to treat disease and aches.

Two such plants share a single name, the pennyroyals. European pennyroyal (Mentha pulegium) is a perennial native to Europe and Western Asia, while American pennyroyal (Hedeoma pulegioides) grows as an annual native to the eastern U.S. Both of these pennyroyals are low-growing, aromatic herbs used by colonists as insect repellents. One visible difference between the two is that European pennyroyal has four stamens, and American pennyroyal blossoms have just two stamens.

Of the two, the European pennyroyal, Mentha pulegium, seems the best. The crushed leaves have a heady fragrance similar to spearmint. It is a traditional culinary herb used to flavor wine in ancient Greece and later in kitchens of the Middle Ages.

While some use pennyroyal leaves in herbal teas, it is toxic to the liver, and can be fatal to infants and children - a good reason to avoid pennyroyal oil, often sold over the counter. Pennyroyal is best as an interesting garden plant and a natural insect repellent.

You can grow pennyroyal from seeds, cuttings or by dividing existing plants in the spring.

If you sow seeds, do not cover them, because the seeds need light to germinate.

Sow the seed in full sun or partial shade after all danger of frost has passed. Lightly mist the seedbed, being careful not to wash away the seeds. You should see seedlings in about two weeks.

You may need to divide pennyroyal plants every three or four years. Do this in early spring before the plants have begun growing.

If you are sowing the seeds indoors, gently sow them on top of the potting soil. Because they need light to germinate, be sure you do not cover the seeds. Place the planted flats or pots where they will get lots of light or use grow lights.

When the plants have at least two sets of true leaves you can transplant them into the outside garden. As the pennyroyal grows you can pinch the growing tips to encourage bushiness.

You can even use pennyroyal as a ground cover in poor soil.

To keep flies, gnats and mice away, colonists planted pennyroyal around their farms and homes. To use as an insect repellent, rub the leaves on your clothing rather than on your skin. Because of its strong oils always always wash your hands after working with pennyroyal.

So whatever became of those few rare 1792 silver center pennies? One 1792 silver center penny sold in 2012 for $1,150,000. Now that is a pretty penny.

Pennyroyal, the smallest member of the Mint family, is a world renowned medicinal herb with a pungent aroma and acrid flavor. Preferring moist, low laying areas this herb is also known as "Lurk in the Ditch" because of its fondness of ditches and swamps.

Pennyroyal has been highly regarded throughout traditional medicine for its effectiveness in treating colds, bloating and spasms. Used as a repellent for fleas in Ancient Rome, Pennyroyal was thought to purify air and water and was hung in the rooms of sick people because of its strong aroma. Still used in modern herbal medicine as an abortificant when brewed to create Pennyroyal Tea, Pennyroyal affects the uterine muscles which contract to cause an abortion. Because of this outcome, pregnant women and people who suffer from kidney or liver problems should not handle or use Pennyroyal.

The more concentrated essential oils of the Pennyroyal plant should never be ingested or taken internally as it is highly poisonous even in small doses. When taken in this manner, the oils cause organs and bodily functions to cease, resulting in an unpleasant death. Consult an herbalist or doctor before using Pennyroyal to avoid bodily harm.

Pennyroyal grows similarly to Mint and produces pretty lavender blooms.


Sometimes Confused With

2.  Hedeoma pulegioides (L.) Pers. N

American false pennyroyal. Cunila pulegioides L. Melissa pulegioides (L.) L. • CT, MA, ME, NH, 
 RI, VT. Fields, roadsides, ledges, trail edges.

All images and text В© 2021 Native Plant Trust or respective copyright holders. All rights reserved.

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Framingham , Massachusetts 01701 USA

The Go Botany project is supported in part by the National Science Foundation.

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