Odorless and non-toxic Earthworm Castings are a natural organic fertilizer and outstanding soil amendment. Will not wash out with watering or burn delicate plants. Castings rival chemical fertilizers in their nutrient composition by providing a concentrated source of calcium, magnesium and nitrogen. Castings are safe – use them for annuals, perennials, seedlings, even cacti and succulents with no danger of chemical harm to your plants or yourself. Indoors, use one part castings to three parts potting soil; outdoors, line the bottom of your hole or furrow with three inches of castings.