From my book Roots Demystified, Change Your Gardening Habits to Help Roots Thrive.
Nature builds soil from the top down with all the decomposition of carbonaceous materials such as fallen leaves and decaying grasses, as well as various forms of feces. In addition, there’s a lot going on, root-wise, beneath the surface of the soil that helps it improve without cultivation. The activities of roots loosen the soil; the roots of nitrogen-fixing plants add nitrogen; “compost” is created as roots rot at all levels to create decomposed organic matter for the use of other plants and microbes; nutrients cycle from root systems to the foliage of plants (and back to the earth again as leaf, stem, branch and trunk litter); roots develop tunnels for the movement of earthworms, root canals help rainwater soak into deeper areas and root exudates create a microbial “soup” which helps to liberate all manner of nutrients.
Sheet composting offers an easy way to improve the garden's soil without strenuous digging. The technique is akin to Ruth Stout's deep mulching practices. Sheet composting has nothing to do with woven percale or thread counts, but refers to the use of thin layers of compostable material laid out over the soil like a thick mulch. By layering high-carbon wastes with nitrogenous plant refuse, you essentially construct a thin, wide, two-dimensional compost pile. Use a blend of dry brown leaves or woody stems (chipped, chopped, or not); fresh grass clippings; green-manure crops such as buckwheat, vetch, bell beans, and clover; wet kitchen garbage or scraps (no meat scraps, as they’ll tend to attract hungry animals and/or smell bad); and green weeds from the garden before their seeds ripen.
Experiment with a ratio of one part green matter to three or four parts dry dead matter. Water the dry materials as you’re layering. At each planting location, make a large planting pocket in the native soil to receive the roots. NOTE: sheet composting doesn't generate enough heat to kill weed seeds, diseases, or pathogens, so after planting, water everything again, then cover the area with five to ten sheets of newspaper, and the newspaper with a weed-free mulch; this should take care of the nasties. The sheet composting slowly helps improve soils from the top down while allowing the gardener to quickly dispose of large quantities of compostable materials and avoid unnatural tillage. The sheet-composted area will require more irrigation the first year or two as the roots grow into the uncultivated soil.
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