Spearmint is a leafy flowering plant most known for its culinary uses. It's a common garnish for many dishes and can be used for flavoring soups, teas and desserts. It is also a natural breath freshener. Spearmint is exceptionally easy to grow outdoors but can be grown indoors as well. This plant likes a lot of light and very good drainage. Too little light and/or soggy soil can kill it. If things go well, however, you'll have more than enough spearmint on hand for many years.
Place the planter pot you intend to use for the spearmint near a sunny window (or use a window sill planter). Add one inch of gravel at the bottom of the pot. According to West Virginia University Extension Service, this will assist in better drainage for indoor plants.
Add loamy potting soil to the pot, filling it to one inch below the rim. General bagged potting soil for house plants is usually suitable. If the soil mix feels dense or heavy, add some sphagnum moss and/or vermiculite to lighten it up.
Dampen the soil by watering with a watering can. Place seeds in the pot with a little soil covering each seed. Plant several seeds in the pot at once in case some fail to germinate (which often happens). You can always thin the plant later. It will take approximately two weeks before you see the seed sprouting. During that time, keep the area well lit with sunlight and fluorescent lights or grow lamps. Keep the soil moist but not overly wet.
Fertilize the spearmint after it has begun to grow. Use either a liquid fertilizer, or stick a fertilizer stick in the pot. Avoid getting fertilizer on the leaves or stem because this can burn the plant. it is better to add fertilizer to the soil (or to a cup of water) and water it in to dilute it.
Water the spearmint, once it is established, once or twice a week. Do not over water the plant or it will rot (and/or develop fungal diseases, as most plants will if over watered). A good, less frequent but thorough watering (that goes all the way down through the pot and drains into the drain pan) is better than daily shallow watering.
Repot the spearmint plant to a larger pot when it begins to overgrow its pot. If your spearmint has really taken off, you may need to thin it a little. You can separate shoots from the root ball for friends to plant if you wish.