Pennyroyal is a perennial herb that is related to the mint family. Its low growing nature and colorful blooms, which can range from reddish purple to lilac, makes this plant a favorite for the herb garden and around the home. But since it is related to the mint family, it can quickly become invasive. To solve this, either control growth through a tough border that the pennyroyal cannot grow through or plant in a container.
Pennyroyal comes in two different varieties that with a quick glance cannot be distinguished. The European variety has four stamens, which is the pollen producing reproductive organ. The American variety only has two stamens and a square stem.
Both types can be grown inside and out. The European pennyroyal has more of a trailing growth habit, which is very conducive to a vertical garden or hanging basket. American pennyroyal works well in container gardens mixed with other herbs and flowers.
Regardless of the variety that you choose, you can start pennyroyal in three ways. The first way is through seeds. These can be purchased from seed catalogues and/or harvested from a friend’s plants. If you purchase your seeds and do not plan to plant immediately, make sure to store them in a cool place away from sunlight.
If, on the other hand, you plan to plant as soon as they arrive, then you will need to prepare to gather your materials. A good all-purpose soil and a flat or container will get you started. The day the seeds arrive, sterilize your container by scrubbing it with an old brush to remove any dirt or hard water stains. Once that is done, place in a bucket of water with a capful of bleach added. Let soak it for 5 to 10 minutes and then rinse. Allow to completely dry out in the sun. Not only will the sun speed up the drying process, it will also sterilize the container beyond what the bleach was able to do.
If using a pot, place a paper coffee filter in the bottom of the container. This will act as drainage material. If you are using a flat, skip the step above.
Once this is done, place your potting soil in the container/flat and moisten with water. Continue to moisten until moisture comes out of the bottom. Now you are ready to plant your seeds, which can simply be sprinkled on the surface of the soil and lightly covered with ¼ inch of soil. Mist with chamomile tea that has cooled. This simple step will prevent damping off, which a fatal fungal disease that seedlings get from being too wet.
At this point, you can cover with clear plastic wrap or leave uncovered. Place in a location that does not receive indirect or no sunlight. Believe it or not, not all seeds require sunlight to germinate. But they do require an evenly moist environment that is warm, so do not be afraid to place your seeds away from the light.
Once you begin to see little green dots appear, remove the plastic wrap if it was used and move to the light. Continue to monitor the soil moisture and water as needed.
If you are going to harvest your own seeds, wait until the plant blooms. Once the flower heads have turned brown, cut the flower stalks so that they are about 6 inches in length. Then, place them in a paper bag, tie the bag off, and hang in a well-ventilated to dry. Once dry, the seeds will fall into the bag and then you can plant.
The second way pennyroyal can be propagated is through division. This is easily done by removing your pennyroyal from its container or if planted in the ground from its confinement. Now, take a knife or use your hands and tear down through the root dividing the plant as many times as you would like. Replant in the ground or plant as described previously.
The third way to propagate pennyroyal is through stem cuttings. Pennyroyal is covered with little white hairs that cover the stem and leaves. These little hairs when encouraged to do so will turn into roots. This can be done in two different ways. One a simple water rooting method can be employed. This is done by cutting the step about to six inches long at an angle. Once that is done, cut the stem again and then place in a glass of water. Change the water at least every other day until you begin to see roots appear.
Another approach to use is to root in the soil. This can be done by taking a cut as above and dipping the cut end in a rooting hormone or honey. Then poke a hole in the prepared pot and place the stem. Gently push the soil together and water in.
For both methods described above, always remove any leaves along the stem that may touch the water or soil.
Regardless of which propagation method you choose, there will come a time that you want to move your plant outside. This should be done gradually over a two week period after your local frost-free date. Once this has been done, it is time to display in its container or plant outside. As far as the container garden aspect, this has been covered previously but this herb’s outside requirements have not been covered. The herb pennyroyal will survive outside in USDA Plant Hardiness Zones 6 through 9. It goes to a height of 18 inches so plan your garden space accordingly. This plant loves a loamy soil that is moist but not wet and one that receives partial shade.
Since pennyroyal is considered an invasive species, you will need to confine it somehow. The type of confinement you use will need to be more than a border. A rubber landscape trim that can be forced into the ground will work. Another idea is to bury your pot in the ground. But if you do this, make sure the container is large enough to hold the plant for a couple of growing seasons. The last idea is to use cinder blocks. The open squares on the side are perfect for plants and the concrete sides will keep the roots of this herb contained.
Pennyroyal is not only a beautiful plant but also a well-known insect repellent. Colonists planted this herb around the foundation of their homes. This simple act kept mice, flies, and fleas out of the home. While pennyroyal is an excellent insect repellent it is a dangerous plant especially for women. To prevent any problem, always wash your hands after handling any part of the plant.