Spearmint is a perennial that is very easy to grow but very INVASIVE!!! I highly recommend that you do NOT plant it in your herb garden because it will take over! If you don’t keep in under control, it will start showing up everywhere (in the above picture, the spearmint is growing between the chives and basil on top and the thyme and oregano on the bottom). To help deter the spearmint from spreading, you can mulch the bed.
How invasive is it?? I even removed the mother plant, and it is still producing spearmint. You really have two options to prevent the spearmint from spreading: 1) plant a pot of spearmint in the herb garden by burying the pot but you better make sure the container is not cracked and doesn’t have any drainage holes or 2) just plant the spearmint in a container. One problem with growing it in a container is that spearmint needs lots of water.
Pinch off the flowers and give the spearmint a “haircut” to extend the harvesting season. We use our fresh spearmint for mojito cocktails and tea.
You can also preserve the leaves by cutting a few branches and hanging upside down in a warm, dry place . Once the leaves are brittle, separate the leave from the stem and crumble the dried leaves Store them in a glass container in a pantry.