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Mint is difficult to grow from seed, and it is virtually impossible for some varieties, like peppermint. Cut a 4 inch (10 cm) sprig about ½ inch (1 cm) above a junction to allow new branches to grow in its place. The sprig does not need to have many leaves, and almost any sprig will do. Place the sprig in a glass of water, and remove any leaves that fall below the water line. Within a week, small white roots should appear under water. Wait a few more days to another week to allow the roots to develop into a decent length.  Add water to the glass as necessary. Make sure that you change the water every four to five days to prevent rot. You can find mint seedlings at most nurseries and garden stores. There are many varieties of mint, such as sweet mint, chocolate mint, spearmint, lemon mint, apple mint, and peppermint. Spearmint is most commonly used for cooking. Mint is a fast-growing, fast-spreading plant and is perfect for one of your first attempts at growing plants. Runners are long stems that grow away from the current plant and set their own roots in the ground. These can be carefully dug up and transplanted. If you have a friend growing mint, the plants will have runners that could be transplanted.
Take a cutting from a pre-existing mint plant. Purchase a mint seedling or small mint plant. Find a runner from a current plant.