Grow amazing houseplants with Miracle-Gro Indoor Potting Mix for All Plants. Blended for a wide variety of indoor container plants, this potting soil is designed to be less prone to gnats because it contains no compost or bark, which are known to shelter fungus gnats. Feeds plants for up to 6 months. One 6 quart bag fills (4) 6-inch containers (exact amounts may vary depending on the size of the root ball).