Mint is one of those plants that will take over your yard if you let it. It is extremely invasive which is why the best way to grow it is in a container. Just buy a small plant and transfer it to a ceramic pot or whatever you have. Place it in a sunny window that gets morning sun but is not too hot. You can also place it on the patio. Then the next time you need mint it will be readily available to pinch off a few sprigs. No rushing to the store at the last minute.