Worm castings are soil or compost that had passed through an earthworm. What comes out contains 5x more nitrogen, 2x more calcium, 7x more phosphorus and potassium and many minerals and beneficial microorganisms all in water-soluble and plant-available forms. Worm “manure” will not burn and is safe for all plants, including houseplants. Worm castings support growth, root development, and disease resistance.