After that, begin layering organic matter on top of the site. Combine materials as you would in a compost pile, by mixing “browns” and “greens.” Add layers of organic materials such as grass clippings, finished compost, chopped leaves, kitchen scraps, coffee grounds, seaweed, shredded mail or newspaper, garden trimmings, used potting soil, sawdust, and weeds (don’t add ones that have gone to seed or perennials with vigorous rhizomes, which will spread and grow in the bed). You can also add topsoil, which will help speed things along. Make a pile that is 1 feet or more deep, and top it off with a layer of mulch to keep weeds from getting a foothold. Then wait several months for materials to decompose.