By Matt Gibson
All About Pennyroyal
European Pennyroyal is also commonly known as churchwort, stinking balm, mosquito mint, squaw mint, flea mint, pudding grass, and organ herb. Pennyroyal hails from the Lamiaceae plant family, specifically from the Mentha genus, which also houses Spearmint, Peppermint, and over a dozen other minty varieties.
Mentha plants are generally fragrant flowering herbs, and Mentha pulegium, or pennyroyal, is no different. It is an aromatic, low-growing, creeping perennial with medium-green, toothed leaves and a blend of upright and spreading stems that support small, tubular, lilac or lavender blooms throughout the summer months. Pennyroyal’s light purple flowers attract butterflies to the garden (butterflies are not harmed by ingesting pennyroyal pollen). The plant’s spreading nature makes it a great choice for filling in any empty spots in garden beds and containers. Plus, whatever plants you border with pennyroyal will also receive it’s pest-deterring protective powers as a neighborly gift.
Growing pennyroyal is easy and rewarding. The vigorous herb is incredibly adaptable to different growing environments, and tolerant of just about anything except for dry soil. As long as you provide a moist bed of soil, European pennyroyal will grow abundantly. Adding pennyroyal to your vegetable garden to deter harmful pests can also greatly improve your chances of producing unmolested harvests.
Household Uses of Pennyroyal
Pennyroyal should never be ingested for any reason, due to its toxicity. However, the plant still holds several valuable household uses. The leaves of the pennyroyal plant can be dried and put in and around the bedding of your pet to deter fleas. Pennyroyal oil was once used on flea collars, but has been taken off the market because it has caused feline miscarriages. If you have pets, keep them safe by only using fresh or dried leaves from the pennyroyal plant for any form of pest management.
Dogs seem to be inherently aware of pennyroyal’s pest deterring powers, as they have been known to roll around in a pennyroyal patch to absorb its fragrance. Crushed pennyroyal stems are quite pungent. Put them in your pockets or stuffed into your handkerchief to ward off mosquitos and gnats.
Pennyroyal plants are also valuable pest deterrents when planted in the garden as companion plants to pest-prone crops. More research is needed, but gardeners have been successful when underplanting pest-prone crops, such as eggplant with pennyroyal plants to discourage flea beetles from damaging their eggplant harvests. Like many relatives of the mint plant, European pennyroyal is a little bit invasive. Be prepared to cut it back when necessary or plant it in an area that has strong, deep reaching borders to keep pennyroyal’s vigorous roots from growing into areas where it isn’t wanted. For a less invasive pest deterrent presence, try growing American pennyroyal in the garden beds. Both species of pennyroyal attract pollinators like bees and butterflies, as well as other beneficial garden insects.
Varieties of Pennyroyal
There are only two varieties of pennyroyal plants, European pennyroyal and American Pennyroyal. Both of the two species contain the toxic compound pulegone, so both can be used to produce flea and pest repellent products, and both plants have pest deterrent aromas, making them good companion plants. Mentha pulegium, a mint relative, is commonly known as European pennyroyal, and is labeled the true pennyroyal cultivar. European pennyroyal, unlike its counterpart, is somewhat invasive, and should be relegated to its desired location by growing it in planters or in garden areas with well-established borders.
Hedeoma pulegioides, commonly called American pennyroyal, false pennyroyal and mock pennyroyal, shares many similarities with European pennyroyal, including the pungent, minty aroma, but is not a mint relative. Both varieties are ground covers with hairy stems. The two pennyroyals can be distinguished by the number of stamens their flowers contain. The European variety has four, while the American species contains only two.
Growing Conditions for European Pennyroyal
European pennyroyal enjoys partial sunlight, but will tolerate full sun locations provided that the soil is consistently moistened. European pennyroyal thrives in steadily moist, well-draining, loamy soil with a pH between 5.5 and 7.0. Though it will adapt well to poor soil conditions, European pennyroyal will grow best in a rich soil that is high in organic matter, so feel free to amend your beds with well-rotted compost before planting.
European pennyroyal will thrive in cool summer weather or hot summer weather. It prefers humidity to dry desert air conditions, but it will adapt to dry air climates if it is well watered. Pay close attention to potted pennyroyal plants to ensure that they don’t dry out or become overheated.
How to Plant European Pennyroyal
European pennyroyal can be germinated indoors or outdoors with high success rates, but we suggest starting your plants inside so that you can better monitor moisture levels in the soil. Provide a light source to help encourage germination. Sow seeds by pressing them gently into slightly damp soil, but leaving them uncovered. Mist the soil with a spray bottle to keep the seeds from drying out, keeping the surface of the soil moist at all times.
Plant seeds directly into the garden after the last frost of the spring or indoors in containers providing soil temperatures between 65 and 70 degrees for germination. Seedlings should begin to sprout up after seven to 21 days, usually around 14 to 15 days if the ideal temperature and environment is provided. Sow or thin European pennyroyal six inches apart. Transplant seedlings outdoors after they develop a second set of “true” leaves and all threat of frost has passed in your area.
Plant European pennyroyal next to any plant that needs help deterring pests. There are no plants that don’t grow well next to European pennyroyal, but due to its pest repelling abilities, the herb is especially beneficial when planted near cabbage, kale, and cauliflower. Since pennyroyal is especially toxic to cats, keep it far away from catnip or catmint plants, so neighborhood cats don’t wander into a pennyroyal patch in pursuit of their favorite plants.
Care for European Pennyroyal
Provide European pennyroyal with regular waterings, keeping the surface of the soil moist at all times. Pennyroyal thrives naturally on stream banks and in other low-lying places where the soil is always moist.
European pennyroyal doesn’t need a boost from any chemical fertilizers. Instead, the herb prefers to get its nutrition from soils rich in organic matter. Soils amended with manure, compost, or leaf mold, will provide pennyroyal plants with all the nutrition needed to grow vigorously throughout the year. Too much fertilizer in the soil will slow or even stop pennyroyal from producing flowers.
Trim back your European pennyroyal to keep it from spreading out too far. Pull up the edges where it is rooting and spreading and trim as needed to keep it where you want it. Pruning [https://www.gardeningchannel.com/pruning-tips/] back your pennyroyal plants may be a necessary task weekly in warm, wet conditions. Cutting back pennyroyal after blooms die back helps keep the plants free of debris also.
Pennyroyal grows well in any sized container, and will even tolerate being root bound. Pick a pot with adequate drainage and fill with commercial potting soil. Keep an eye on the roots creeping through the drainage holes and into the ground below, because whoever made pennyroyal forgot to put in the quit.
How to Propagate European Pennyroyal
Propagating pennyroyal can be done by division, cuttings, or by layering. The simplest propagation method is to dig up a piece of pennyroyal and plant it in a new location in moist soil. Pennyroyal naturally forms roots all along its stem while spreading. Removing a piece of the plant from the roots up allows you to start with a piece of the plant that has already started forming roots. For this reason, propagating by division is the easiest way to make new pennyroyal plants. Divide pennyroyal plants every three years to keep plants growing healthily.
Propagating from cuttings is fairly easy as well. Tip cuttings will easily root in moist soil or a vase of water. Branch cuttings can also be encouraged to root by dipping them in a rooting hormone and putting the cut end into moist soil. After it starts to root, plant it in a light, moist potting mix and wait for it to develop new leaves before transplanting it outside.
Another way to propagate European pennyroyal is to mimic the way in which the plant naturally reproduces. To propagate pennyroyal by layering, just bend a branch and cover it with about an inch of soil. Then, place a small stone above to hold down the buried branch and encourage moisture retention in the area. Soon, the end of the branch will start to develop new growth. At this point, you can cut the old branch where it starts to go into the soil.
Garden Pests and Diseases of European Pennyroyal
Due to its aromatic pest repelling capabilities, there are few insects that dare to trouble the European pennyroyal. Pennyroyal is also generally free of root or leaf diseases as long as it is provided with a well-draining soil medium. However, two common plant diseases occasionally trouble European pennyroyal plants when they are growing in an overcrowded, overly-wet, shaded environment. Powdery mildew and mint rust can become a problem in environments like these. To prevent these diseases, keep your pennyroyal plants well-draining soil and in locations that receive plenty of sun. Additionally, space your pennyroyal plants out properly to promote better air circulation.
How to Harvest European Pennyroyal
The pruned stems and the dried stems and leaves of the pennyroyal plant can be used to repel common pests. Place cut stems and dried leaves wherever you have a pest problem, or toss them into pest-repelling potpourri baskets.
Though European pennyroyal is highly toxic when ingested, the aromatic herb still has plenty of beneficial qualities and can be put to use in the garden and in general pest management. The herb is easy to grow, perfect for filling in bare spots in garden beds or containers. European pennyroyal is versatile, highly-adaptable, and a great companion plant for a variety of pest-prone garden favorites.
Medicine hasn’t always been as scientifically informed as it is today. Pennyroyal has a long history of medicinal use for various ailments, but medical science has proven that pennyroyal is highly toxic and not at all safe for humans to ingest. Taking pennyroyal internally can harm the liver and kidney, and can even be fatal. It should have been pretty obvious that pennyroyal is toxic, considering it was used as an abortion remedy over 2000 years ago.
The essential oil made from European Pennyroyal and American Pennyroyal flowers is especially toxic, and is strong enough to be considered a lethal poison. A college student died from drinking tea made with pennyroyal oil over a two day period in 1994. He only ingested 2 teaspoons of the oil during that time. The active ingredient in both species of pennyroyal is pulegone. The compound has been used culinarily as a flavoring agent, medicinally, namely as a cold remedy. Thankfully, pennyroyal’s toxicity is now commonly known, so pennyroyal is no longer used for culinary or medicinal purposes.
Despite the toxicity, pennyroyal still has a few household uses. Pennyroyal, specifically the compound pulegone, is used to make flea deterrent, pest repellant, and it can be planted in the garden around pest-prone plants to protect them from infestations.