Will The Strong Scent Of Pennyroyal Banish Squirrels From A Bird Feeder?

American pennyroyal (Hedeoma pulegioides) has a remarkably strong scent for such a small and unassuming plant. At most, it grows a foot tall, and its leaves are only an inch long. Tiny white or blue-violet flowers grow at the base of those leaves, blooming from mid-summer to early fall and attracting small pollinators like bees. The pleasing aroma of the modest pennyroyal, however, is a significant deterrent to some wildlife. Plant-eating mammals from cows to squirrels are said to be repelled by the strong smell. 

Pennyroyal is a member of the mint family, and peppermint is frequently touted as a way to get rid of squirrels. Peppermint oil is so frequently used to deter rodents that many big-box stores sell commercial products made with it. Since pennyroyal is a mint with a strong scent, it's sensible to assume it should repel squirrels from your bird feeder. However, peppermint oil is not toxic except in very large doses, while pennyroyal oil is highly toxic. The evidence of pennyroyal's usefulness is much more anecdotal than scientific. For example, a 1995 study presented at the National Wildlife Research Center Repellents Conference compared the efficacy of different scents in repelling woodchucks; it ultimately found that aromas like geranium and coyote urine were far more effective than pennyroyal. 

Growing pennyroyal around the base of your bird feeder may deter squirrels from climbing up the post. The plant, hardy in zones 5 to 9, is an annual that prefers dry, sandy soil and full or partial sun. It can tolerate dry conditions, but the spreading, low-lying plant won't thrive where there is competition from taller vegetation. American pennyroyal and European pennyroyal (Mentha pulegium) are very similar plants, though the European variety is a perennial. It also has a very strong scent that may be a deterrent to squirrels, and, like American pennyroyal, can be useful as an insecticide ingredient. 

Like many plants with medicinal properties, pennyroyal's uses can be traced to ancient Greek and Roman times when it was used as an insecticide, abortifacient, and cooking herb. In more modern times, the Dakota used false pennyroyal (Hedeoma hispida) to treat colds. Despite its medicinal applications, the concentrated oil of pennyroyal should be handled with extreme caution. It contains pulegone, a toxin found in the plant that's used in some tobacco products to impart a menthol flavor. Pulegone is a carcinogen that's fatal to humans, even in doses as small as one tablespoon when eaten. While you can buy pennyroyal essential oil, it's wise not to use it to repel or kill squirrels because of its danger to children and pets. There are safer and better ways to keep squirrels out of your bird feeder.