How to Propagate Mint Plants

If you've had a "patch" of mint (Mentha spp.) for several years, the question is not how to propagate the herb but how to control it. Mint spreads by underground runners, called rhizomes. Some varieties, including spearmint (Mentha spicata) and peppermint (Mentha x peperita), which grow in U.S. Department of Agriculture plant hardiness zones 5 through 9, spread aggressively, becoming invasive in gardens and lawns. Propagate this herb by seed, cuttings or division.

The most-labor intensive way too propagate mint is by seed. Store seeds collected from plants in fall in the refrigerator vegetable crisper for spring planting. This is not foolproof -- hybrid plant seeds might be sterile and mints hybridize easily with each other, so buying seeds is your best bet for getting the specific mint you want. Start seeds indoors in pots two months before the last frost or sow mint seeds directly in the garden -- it's a fast grower. Use pots with drainage holes to ensure good drainage.

When the soil begins to warm above 60 degrees Fahrenheit after the last frost, work the soil into a fine texture to a depth of at least 12 inches. Add a 1- or 2-inch layer of peat moss or compost to heavy or clay soil and work it thoroughly into the soil. Scatter mint seed and bury it twice the depth of the seed -- about 1/4 inch. Keep the soil moist until the mint has sprouted. Thin young plants, allowing 4 to 6 inches between plants.

Take cuttings in spring or early summer. Cut 3- to 4-inch segments of mint just above nodes -- the thickened areas on the stems from which the leaves grow. Wipe the cutting tool with a cloth soaked in rubbing alcohol to prevent the spread of disease. Remove all but four or five leaves from the bottom of the cuttings and keep the cuttings in a glass of water for seven to 10 days until tiny roots start forming at the nodes. When the new roots are 1 to 2 inches long, plant them in pots or the garden. Use pots that have drainage holes.

Dig3-inch-square divisions from an existing mint patch in spring after the last frost. Trim top growth back to 4 to 5 inches and snip scraggly roots hanging from the root ball -- you can plant them separately. Find a sunny spot and cultivate the soil deeply. Add enough compost to give it a fine, crumbly texture to provide good drainage. Dig a hole as deep as the root ball and rough up its surface to encourage rhizomes to spread outward.

Set the division in the hole about 1/2 inch lower than it sat previously and fill in soil around it. Water deeply and keep the ground moist for a week or two until new growth begins. When planting multiple divisions, space them 8 to 10 inches apart.

A successful mint patch requires well-draining, evenly moist soil, perhaps near a downspout at the corner of the house in bright light where it gets sun in the morning or afternoon. You don't have to give mint the prime spot in the garden. It soaks up moisture in wet areas and checks erosion on hard-to-mow hills.

Whether getting cuttings from a fellow gardener or shopping at a nursery center, chose a mint that's right for your climate. Less hardy mints, such as pineapple mint (Mentha suaveolens "Variegata") and Corsican mint (Mentha requienii), which grow in USDA zones 6 through 9, or little pennyroyal (Mentha pulegium), which grows in USDA zone 6 through 11, may be only marginally hardy in your area. Variegated mints, such as pineapple mint, need partial shade.