It all begins with the soil. Worms are the great transformers of landscape through eating and digesting. They can consume a patch of stones and over time turn it into a fertile field. Worms continually pass soil through their intestinal canals, keep anything they can use for food, and then "cast" the rest. With indoor worm composters, these creatures can take your coffee grinds, lettuce scraps and apple cores and turn them into fertilizer castings that your plants will love.