Lawn clippings, compost, dead leaves, stems from other dead plants and manure are terrific additives. Take care not to use any plant materials that are bug infested or diseased since they will contaminate the soil or could cause problems in the future. Organic mulch that has been used on your garden during the summer months should be plowed under at the end of each season. Alfalfa, rye and clover, which are known as green manure, have nitrogen fixing bacteria growing in their roots. These are perfect organic matter and can be grown in separate patches for this purpose.
Organic matter is beneficial to organisms in the soil and provide a rich food for earthworms.
For the best results mix organic matter into only the first 12 inches of your soil. If your soil has too much clay add coarse sand and redwood bark shavings. This will aerate the soil and improve the soil structure. If you soil is too sandy add sphagnum or peat moss with your organic matter. This aids the soil in retaining moisture and will increase the nutrient holding capacity in the soil.