Are you looking for a sprawling ground cover that emits a delicious scent when it's crushed under your naked toes? How about a long-blooming, showy accent for your multi-species container garden?
An ornamental perennial and member of the Lamiaceae family, pennyroyal is native to southern Europe, North Africa, and the Middle East. There are a few different herbs bearing the same name, but Mentha pulegium, or "European pennyroyal", is the real deal.
As you'll read below, we don't recommend this plant as a medicinal herb, but it more than makes up for its one-trick wonders when you use it as an ornamental.
Pennyroyal in the Garden
Think of pennyroyal as the runt of the mint litter. A more flattering description paints pennyroyal as a low-growing, spreading plant, with growing habits much like creeping thyme. When planted in pots or hanging baskets, pennyroyal will delicately cascade over the sides of the container.
Pennyroyal's branching stems are woody, with a cream to chestnut color, sometimes with a faint lilac tint; its tiny dark green leaves are elliptical in shape, forming on opposite pairs directly from the stem. The leaves have a few hairs, but aren't fuzzy; in fact, the leaves along the woodier parts of the stalks can have a waxy appearance.
It generally only grows an inch or two tall when it's not in bloom, and can spread about three feet outward. After a few seasons, it might naturally propagate in a radial pattern, leaving the center bare; simply fill it in with new seedlings or layered cuttings.
Flowers and Bloom Period: Mentha pulegium's pink to purple flowers—forming ruffly whorls along each plant's upward-growing terminal spikes— bloom from June through October in the most temperate zones, extending the beauty of your garden and providing pollinators with plenty of reasons to stick around.
Fragrance and Flavor: Pennyroyal is perhaps the most fragrant of the mints when you crush its tiny leaves between your fingers. Some have described it as having a "vanilla peppermint" aroma. It might smell delicious, but... wait for it...
Herbal Uses: Achtung, Baby!
Concentrated pennyroyal oil, which contains a potentially deadly substance called pulegone, is considered highly toxic when ingested, according to National Capital Poison Center. Absorption through the skin is also hazardous, especially to animals and kids. In spite of its long history as a medicinal herb and flavoring, We don't recommend the use of any part of the plant for teas or seasonings.
Pennyroyal has a reputation for repelling fleas, so be wary of natural flea sprays and powders containing pennyroyal. Remember: "natural" doesn't always mean "healthy", and sometimes, it can be downright dangerous. While it may indeed repel insect pests, fleas don't hang around on dogs and cats that go "paws up", and we're not sure how well pennyroyal wards off blowflies and maggots. Yep, we went there, but we're trying to make a point, especially since there's so much misinformation floating around about pennyroyal's "all natural" solution to flea and mosquito control.
For an interesting and cautionary article about pennyroyal's toxicity to pets that includes a summary of a 1992 study on the subject, check out this link to Dogs Naturally Magazine.
Relatively Safe Uses for Pennyroyal
Some gardeners will rub pennyroyal leaves on their clothing to repel mosquitoes; just be sure to wash your hands afterward.
You might consider planting pennyroyal around the foundations of buildings and garbage can storage areas, as it does repel rodents and ants. When planted near standing water, it discourages mosquitoes from breeding.
Sachets made from dried pennyroyal can keep mice out of cupboards, pantries, or sock drawers; we suggest you mark them so you don't end up dumping their contents (the sachets, duh) in your lamb stew.
One Final Caution
Children and animals are more sensitive to toxic substances than are grownups, and ingesting pennyroyal in plant form, or allowing dermal contact with pennyroyal oil, can result in poisoning symptoms. If your kids (or pets) have the habit of shoving random stuff in their mouths, you might choose to grow it out of reach in hanging baskets. If you suspect pennyroyal poisoning, call Poison Control at 1-800-222-1222.
How Did We Manage to Survive as a Species?
People who likely blamed evil spirits and demons for otherwise unexplained illnesses, and who used leeches and bloodletting to cure the vapors, were known to use pennyroyal for the following:
- Menstruation aid (to expel bad spirits and the "other stuff").
- Induce abortion (see above; also see why it's such a bad idea).
- Flatulence, but you can't swing a poisoned cat without hitting an herb that cures the Divine Wind.
- Hysteria, but that's what wine's for.
- Venomous bites, but we're unclear if it was used before the bite—to ward off the biter—or after, to just "end it" once gangrene has set in.
- When added to mattress stuffing, it repelled fleas and other pests. Sexy.
- When sprinkled on library bookshelves, it repelled silverfish.
Doddering apothecaries and ancient, scraggly-haired, wart-nosed midwives likely mumbled the following disclaimer so quickly, they were burned at the stake for speaking in tongues:
"Maycausegastrointestinaldistressnauseavomitingabdominalpainliverandkindeyfailurebleedingseizuresanddeath." — Medieval corporate attorneys
Um, it's cool; we prefer to simply enjoy pennyroyal's beauty in the garden.
Pennyroyal deserves the above warnings, but it's important to use any concentrated herbal remedy with care. We recommend that our customers consult with their physicians before adding alternative (or, for that matter, mainstream) treatments to their wellness regimen.
Growing pennyroyal from seed, either indoors or directly in the garden, is easy in USDA Hardiness Zones 5-9. Unlike other mints, pennyroyal isn't known to be particularly invasive.
In cooler regions, this perennial herb might suffer a bit of frost damage, but it usually grows back the following spring.
The Perfect Spot for Pennyroyal
Pennyroyal prefers moist (yeah, we hate that word too), loamy, well-draining soil and full sun, but tolerates partial shade. While pennyroyal can thrive in poorer soils, it does best with soil amended with fine compost. Aim for pH between 5.5 and 7.0.
Be sure your container-planted pennyroyal doesn't overheat or dry out. Like any groundcover, it helps to keep the soil beneath it cool, so consider using it as a living mulch around other plants.
This herb is great for drip-irrigated rock gardens and borders, and the spaces between pavers or stepping stones.
Planting Pennyroyal Seeds
- Pennyroyal grows easily whether planted indoors or out, though we prefer to start them indoors so we can keep an eye on soil moisture.
- Its seeds need light to germinate, so press them lightly into damp soil, and leave them uncovered. Use a misting bottle to keep them from drying out.
- Plant seeds outdoors after your last Spring frost, or indoors with soil temperatures kept about 65-70°F Germination occurs 7-21 days after planting—usually two weeks under optimal conditions.
- Plant or thin pennyroyal about six inches apart for optimal coverage.
- Once your pennyroyal starts have grown at least two sets of "true" leaves, and your windshield stops icing over every night, they can be transplanted outdoors.
Maintaining and Propagating Pennyroyal
Pennyroyal is fairly easygoing, and aside from requiring moisture and initial soil amendment, you don't have to do much the first few years to keep it happy.
Pests and Diseases: Okey Dokey. We usually try and corroborate our facts with three or more reputable sources, but when we Googled "Pennyroyal's Pests and Diseases" or similar keyword strings, we came up with all sorts of hoo-haw promoting pennyroyal as a topical insect repellent for humans, children, dogs, and cats. I mean... come on. Anyway, overall, pennyroyal isn't prone to insect pests or foliar and root ailments, as long as it's grown in well-drained soil.
Trimming: If you want tidier, fuller plants, pinch off the ends of their branches. In doing so (well before flowering time) you'll also encourage multiple flowering spikes.
You can also trim pennyroyal back to within 3-4 inches of its base early spring or fall for healthy new growth.
Propagating by Division: We recommend dividing pennyroyal every three years for optimal plant health. Around this time, you might want to fill in "leggy" or bare areas with additional plantings.
Propagation by Cuttings: You can use your favorite method for growing new plants from cuttings. Ours is to trim a branch from a healthy plant, dip it in rooting hormone, and place the cut end (as if we have to tell you) in a damp, sterile substrate. Once rooting occurs, place the cutting in a light potting mix, keep it moist, and wait until it's grown new leaves before transplanting outdoors.
Propagation by Layering: This is one way pennyroyal naturally reproduces. Bend a branch and cover it with an inch or so of soil, and place a small stone above to both hold down the layered plant segment and help retain moisture in the immediate area. Once the end of the branch begins showing growth, cut the "old" branch where it enters the soil.
Pennyroyal's Companions: Pennyroyal has no enemies in the plant world, but does especially well with kale, cauliflower, and cabbage, likely because it helps repel pests that usually destroy these crops.
Don't plant pennyroyal near catnip or catmint, since it's particularly toxic to cats and you don't want to draw the attention of jonesing felines.