How to Plant and Grow Peppermint
For most gardeners, the trick to growing peppermint in the garden is keeping it from taking over. Like most members of the mint family, peppermint can become invasive if allowed to grow freely in optimal conditions.
Peppermint (Mentha piperita) is believed to be a hybrid between spearmint and water mint. As a hybrid it rarely produces seeds and most of the seeds it produces are sterile. Like other mints, peppermint spreads vigorously by runners, or stolons, that travel just under the soil surface and emerge as a new plant. The stolons have been known to travel several feet under bricks, rocks, and other barriers and emerge happily in the other side.
While peppermint will grow in almost any soil, it prefers a mild, moist, shady area and rich, loamy, moisture retaining soil. It is often grown in boggy soil and reclaimed swamplands. For the home garden, a location that receives part sun and remains slightly moist without being saturated is ideal.
Plant cuttings or divided plants in the spring and apply a liberal amount of composted manure at planting time. Peppermint enjoys a high nitrogen level which will encourage green leafy growth. Peppermint prefers slightly acidic soil which can be achieved by adding leaf mold or humus during planting and mulching with shredded leaves in the winter. Plants should be planted at least 2 feet apart to allow the plant to spread out.
Peppermint enjoys a consistently moist soil and should receive at least 1 to 2 inches of water per week. However, the ground should not be soggy or it can lead to disease. Watering over the top of plants can also encourage disease and should be avoided. Drip irrigation is one of the best ways to water mint because it keeps the ground moist without wetting the leaves.
Peppermint is hardy to about 20 degrees below zero, but should be mulched heavily in the winter. The mulch can also add nutrients to the soil and encourage healthy plants.
For plants in their second year or beyond, a generous amount of manure or a general purpose 16-16-16 fertilizer should be added at the rate of one teaspoon per plant. Plants can be divided in the spring right before new growth starts. For overgrown, spreading plants, early spring is the best time to thin or divide plants to prevent overgrowth.
Peppermint is not susceptible to many garden pests or diseases. Most pests will leave peppermint alone because of its strong odor, but aphids, cut worms, flea beetles, and other leaf eating insects will attack peppermint. To combat aphids a simple insecticidal soap spray will kill them or a light water blast will knock them off the plant. Cut worms will chew through the stems at or even below ground level, destroying the entire plant until it grows back from the roots. There are traps for cut worms, but it often requires insecticides to get rid of them. Flea beetles are tiny black beetles that will chew tiny holes in the leaves. They are also usually controlled by insecticides.
Peppermint is only commonly susceptible to three plant diseases: anthracnose, verticillium wilt, and mint rust. Anthracnose is distinguished by small wet looking spots on the leaves that can spread throughout a plant and kill it or make the leaves unusable. Anthracnose can be prevented by using good crop rotation techniques and pruning plants in the fall. Verticillium wilt causes leaves to yellow and die. This disease can also be prevented by using good crop rotation techniques and by not over fertilizing. Finally, mint rust starts with small white spots that turn brown or orange and kill the leaves, This can be avoided by not watering over the top of plants, especially when the leaves may remain wet overnight.
In the home garden, two peppermint plants is usually sufficient to supply fresh mint throughout the growing season plus enough dry mint to last through the winter. Begin harvesting in the spring once the plant has reached 3 to 4 inches by cutting the stems back down to almost ground level. Do not allow the plants to bloom, or the oil level will be reduced. Pinch off blossoms before they open and then harvest the leaves.
Pruning mint for the winter will help prevent disease. Just before the first killing frost prune the plants all the way to the ground and mulch with leaf mold.
All species of mint are considered invasive. While peppermint is a hybrid and generally sterile, it can sometimes spread by seed if allowed to blossom. It will also send out stolons and spread rapidly, especially in the second and subsequent growing years. To prevent this, consider growing peppermint in a container and always pinch off blossoms.