How to Grow & Plant European Pennyroyal (Mentha pulegium)


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European pennyroyal mentha pulegium flowers
The small flowers of European pennyroyal are lobed and somewhat tubular to draw in small pollinators, such as bee flies. Photo by Daniel Feliciano, CC BY-SA 4.0

Sometimes known by other names such as mosquito plant, pudding grass, and squaw mint, pennyroyal is an herb in the mint (Lamiaceae) family. This is a large family, which includes many aromatic plants such as sage, rosemary, oregano, thyme, and lavender. Plants in the mint family can be found worldwide. European pennyroyal, the species discussed in this article, specifically is native to Europe, North Africa, and the Middle East.

Pennyroyal produces small clusters of lavender-colored flowers. Crushed pennyroyal leaves have a scent that is often compared to spearmint, a close relative. This species was once commonly used as a medicinal herb and is occasionally used for this reason today. American pennyroyal (Hedeoma pulegoides), native to North America, is often used for the same types of medicinal uses but is from an entirely different family and is not closely related. 

Facts, Benefits & Uses of Pennyroyal

mosquito plant mentha pulegium seeds
The small seeds of pennyroyal provide food for passerine birds and some small mammals in the autumn. Photo by Stefan.lefnaer, CC BY-SA 4.0

Pennyroyal can be used as a natural insect repellent for a variety of insects, including gnats, mosquitoes, and fleas. Planting pennyroyal around your home may help to deter these insects, and pennyroyal oil has even been used in some flea collars for pets. Although it may deter some pests, it is still attractive to pollinators such as bees. Additionally, birds and some small mammals enjoy eating the seeds.

Pennyroyal has a long history as a folk remedy and herb, but this is no longer recommended because it is quite toxic to humans and some animals. This plant has had a wide variety of supposed uses, including everything from headaches to lung conditions. As a fragrant member of the mint family, pennyroyal even was once used in culinary applications, such as to flavor teas or as an herb for cooking.

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Pennyroyal Fact Sheet:
PLANT TYPE
Herbaceous Perennial
HARDINESS ZONES
USDA 6 – 9
LIGHT REQUIREMENTS
Full sun to partial shade
BLOOM COLOR
Purple
BLOOM PERIOD
July – September (Summer)
MAXIMUM GROWTH
Height 15-30 cm (6-12 in.)
PLANTING DEPTH
seeds: on surface of soil; mature plant: 10-15 cm (4-6 in.)
WATER QUALITY
pH 5.0 – 7.0

Pennyroyal Growth, Hardiness & Climate

how fast does squaw mint mentha pulegium grow
If provided with the right conditions, squaw mint can form thick groups that may need to be thinned from time to time. Photo by Raffi Kojian, CC BY-SA 3.0

Pennyroyal is typically found in moist, rich soil, and is an enthusiastic spreader. This plant is generally considered to be easy to grow. Pennyroyal is a versatile plant, and can be used for groundcover, garden edging, and even as a hanging plant. This plant is hardy in zones 6-9 and is a perennial.


How to Plant Pennyroyal In Ponds

how to plant european pennyroyal
Some pennyroyal plants may do just fine in standing water, while younger individuals may prefer moist soil. Photo by Stefan.lefnaer, CC BY-SA 4.0

One option for planting pennyroyal is to grow it from seed. Pennyroyal seeds should be sown on the surface of soil in the spring after any risk of frost has passed. Surface sowing is important for pennyroyal because the seeds require light in order to germinate, which will take roughly two weeks. Pennyroyal can also be propagated from placing cuttings barely below the soil surface or grown by simply burying the roots of a mature plant up to the crowns of the stems. Mature plants can be planted in standing water, but take note that some individuals will do just fine with this while others may prefer just moist soil to being waterlogged.

Pennyroyal is a low-growing plant, and typically does not grow more than six inches above the ground. This plant is generally unassuming but does produce attractive purple flowers in mid-summer and early fall. 


How to Care For Pennyroyal

pennyroyal growing in the sun near a pond
Pennyroyal grows best when grown in full to partial sun. Photo by Stefan.lefnaer, CC BY-SA 4.0

Pennyroyal is low-maintenance and easy to care for. This plant does best in rich, moist soil with access to full to partial sunlight. Be sure that although your pennyroyal’s soil is moist, it still does drain and isn’t waterlogged. As mentioned above, they can grow in standing water but can be a bit picky – some individuals die, while others enjoy the water.

This species can easily spread and become leggy, so you can pinch the ends of the herb occasionally to encourage bushiness. You also can divide established plants every few years to prevent too much spreading.


How to Winter Pennyroyal

Pennyroyal is native to cold areas and is winter hardy in zones 6 through 9. In these areas, pennyroyal does not require any special treatment in order to survive the winter. Some gardeners in colder zones attempt to help their pennyroyal plants survive the winter by laying down a layer of mulch to protect the stems and leaves. However, this will not necessarily be successful. Within pennyroyal’s native hardiness zones, it is a perennial and can be seen in gardens for many years after planting.


Is Pennyroyal Toxic, Poisonous or Invasive?

Pennyroyal is native to Europe, North Africa, and the Middle East, and is considered to be moderately invasive outside of this range. In Australia, it is considered an invasive and noxious weed. It is not known to be an extremely aggressive plant, but, like many plants in the mint family, pennyroyal is an enthusiastic spreader. Take care when planting this species in your garden that it does not take over more area than you want it to. A great option to prevent excessive spreading is to plant pennyroyal in a pot or planter instead of directly into the ground.

Pennyroyal is known to be quite toxic, even though it was consumed by humans throughout history for medicinal and culinary purposes. The most dangerous form of pennyroyal is in concentrated pennyroyal oil, which contains a high percentage of the toxin pulegone. This toxin can cause a variety of problems depending on dosage, which can range from nausea and abdominal pain to lesions and tumors to organ failure. There are documented cases of pennyroyal causing death, mostly when taken in high doses by pregnant women.


Is Pennyroyal Edible? Will Fish Eat it?

The question of whether pennyroyal is edible is a somewhat complicated one—this plant is considered to be toxic but has been ingested by humans for a variety of purposes throughout history. It’s also sometimes used as an extract for mint flavorings. Fortunately, pennyroyal has fallen out of fashion as a medicine and food, but some cultures still do occasionally use it.

Pennyroyal is not known to create any dangers for pond fish in particular, but to be safe, many people choose to keep this plant away from their fish. Planting pennyroyal far enough away from your pond that fish will not be able to access it will ensure that no toxic oils contaminate your pond. This shouldn’t prove difficult or really interfere with how you’d normally plant it, since pennyroyal does not like to be planted directly in water or in muddy, waterlogged areas but rather prefers moist but well-draining locations.


Where to Buy Pennyroyal & Seeds? (UK & US)

Pennyroyal is available at online and in-person nurseries that sell to the plant’s native ranges. In North America, plants marketed as pennyroyal are likely the similar but unrelated American pennyroyal (Hedeoma pulegoides) plant. If you are set on having Mentha pulegium in your garden, you may have to order online, paying special attention to the scientific name of the plant. As always, do try to select plants for your garden that are native to your area.

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