Wiggle Worm Soil Builder? Earthworm Castings Organic Fertilizer is an all purpose natural fertilizer that comes to you straight from nature with no alterations whatsoever. Our nightcrawlers are fed a very rich peat humus which contains a wide variety of minerals and trace elements. The earthworms digest this material and in its passage through the worm, it is beneficially altered both chemically and physically. The nutrients in our earthworm castings are plentiful. Most importantly, these nutrients are perfectly balanced in two forms. One form can be immediately absorbed by the plant as if it were directly injected, and the other form is able to provide nutrition which slowly feeds the plant for long periods of time. Some sizes may not be stocked in all locations.