Worm castings are rich in organic materials and beneficial microbes, resulting in benefits considerably beyond what fertilizer ratios indicate. The organic matter in castings promotes soil structure because it contains low-essential plant nutrients, such as iron. Castings promote soil aeration, boost water retention, and anchor plant nutrients that might otherwise be washed away by water. Organic matter provides food for soil microbes, making, storing, and releasing plant nourishment over time. Worm castings are suitable for use in both indoor and outdoor gardens.