Earth Science 12 lb earthworm castings is the richest, most natural compost available and is naturally non-burning and odorless. worm castings add essential organic matter that increases microbial activity aor a living, nutrient rich soil. use for seed starting, indoor and outdoor plants and gardens including container gardens, trees and shrubs. simply sprinkle a small amount and it will slowly enrich soil with more nutrients than most yard compost without burning plants. all organic, omri listed.