Prune the plant in late spring or early summer when the new growth reaches 4 inches. Remove the stems so only 1 inch of each stem remains on the plant. Leave at least one set of leaves on each stem.
Trim the plant each time it reaches 4 inches if you prefer to keep the plant small. Frequent pruning also prevents mint from outgrowing small pots in container herb gardens.
Allow plants to grow 8 to 12 inches tall after the initial pruning in spring if you prefer a bushier plant. Cut back the stems by up to half each time they reach the desired height.
Cut back the plants throughout the summer. Stop pruning when the plant enters semi-dormancy in late fall and stops putting on new growth. Prune indoor mint plants year-round if they continue to put on new growth through winter.