Answer: Mint spreads both by underground roots and by seeds. You can discourage the plants by cutting them down at ground level whenever they sprout, or by carefully digging the roots out, making sure to get every last inkling of root. Mint can overtake an area in a very short time. You may have to use a combination of cutting and digging until you finally starve the roots out or completely dig them up. The plants are quite resistant to herbicides so digging is the best (and safest) solution, especially when they share a bed with other plants.
Q&A Library Searching Tips