What are worm castings and what difference can they make in my garden? Simply put, castings are worm poop and they are full of top quality fertilizer elements that all plants need. As earthworms move through soil and improve its tilth, they eat, digest, and excrete. This natural process results in poop long heralded as a garden amendment, most notably by the venerable Robert Rodale who wrote about its fine humus qualities. So, the noble earthworms constantly till your soil to loosen it and increase its water management abilities. In the process, they leave poop for your plants that is nutritious and full of microlife. Diligent worm farmers harvest the poop and package it so you can easily add it to soil for garden beds, lawns, and containers. Look for more wormy facts at wormwise.com.