Mint grows profusely and reproduces via long underground roots. If left to its own devices, mint may spread several feet in one year sending up new shoots a foot or more from the original plant. When planted in borders of lawns, mowing the new shoots that invade the lawn keeps it under control and emits intense fragrance as well. When grown in the perennial bed or herb garden, mint can take over but there are ways to prevent it from spreading.
Cut the top and bottom off a one gallon can. Wash and dry the can.
Dig a hole 10 inches deep and a foot in diameter in the prepared garden bed.
Insert the can into the hole so the rim of the can rests slightly above the soil level. Build up soil in the bottom of the hole, if necessary.
Fill the can one-half to three-quartes full with prepared soil from your garden bed.
Place the mint seedling in the center of the can and fill in around the roots with soil. Position the plant so it rests at its original planting depth. Firm down to secure the plant.
Fill in around the outside of the can with soil and pack firmly to hold the can in place.
Water thoroughly and and keep soil moist until new growth appears. Resume normal care by watering deeply once a month and weeding as necessary.