Pennyroyal

The flowers of anise hyssop, catmint, and bee balm have been drawing lots of buzz for most of this summer. Bees and other insects have been busy and there’s been humming and buzzing everywhere as we walk through the gardens. But this is nothing compared to what’s going on with the pennyroyal. Pennyroyal is a ground cover plant that sends up flower stalks about a foot tall, with flowers that are little fuzzy spheres encircling the stalk.

An unidentified bug on pennyroyal

The pennyroyal flowers must be extra-sappy with nectar because they are almost always swarmed with bugs. These are mostly bees; itsy-bitsy ones, medium sized ones and big fat bumbles. One day I happened to notice a really strange looking insect in the pennyroyal. Not quite a Darth Vader of the insect world, but it was nasty-black with some specks of yellow, and with a skinny, thread-like waist. I looked it up. It appears this strange looking thing is a Mud Dauber.

Thanks to the pennyroyal, I am introduced to a new bug. These are some very interesting critters. It seems they prey on spiders and drink nectar. The female lays an egg, enclosing it in a casing made of mud along with a spider numbed by her venom. When the larva hatches its immediate source of food is ... you guessed it, the spider. 

Apparently daubers have a liking for caterpillars. Espying a rose leaf swaying madly back and forth on one of my wanders through the garden, I turned the leaf over. And found a mud dauber looking like it was about to do something nasty to a little green caterpillar. 

Anyway, back to the pennyroyal. What is growing here is Mentha pulegium, or European pennyroyal. Mentha is a genus of plants in the mint family. The European pennyroyal is a ground hugging creeper, and is the shortest plant that I’ve ever seen. Patches of it form solid masses that literally hug the ground. If you are looking for a plant to be a ground cover, this one can cover the ground. It just might be a good weed inhibitor. 

A patch of pennyroyal

Like any of the mints it is said to be potentially invasive. I can see how that would be, because it is establishing itself in hard-packed clayey dirt with no problem whatsoever. Either this is its preference, or it is capable of far greater abundance in amended soil. Growing along the sides of a stone pathway, it shows signs of wanting to creep between the stones. This would be a welcome attribute.

Whatever you do, don’t eat or ingest any part of this plant. Many sources state that it is toxic to the liver and can be deadly, unlike many other of the mints which are edible. Avoid any oil of this plant, as that is especially noted as toxic. My research indicates that small uses of the leaves, fresh or dried may be safe, such as tucking a sprig into clothing for a mosquito repellent, and that dogs might have a tendency to roll in it, protecting themselves from fleas.

Pennyroyal can be purchased as potted plants, or seeds. Mine were started from a packet of seeds. Once planted, it seems to spread almost magically. It is hardy up to zone six, giving it an unreliable hardiness here in zone five. Even though it could disappear in a cold winter, I’d reseed it. Pennyroyal is an interesting plant. -jmm