Several organic amendments are useful in improving the structure of clay soils, thereby improving drainage and aeration; this provides a more healthful environment for plant root systems. Yard waste compost, mushroom compost, animal manures, composted sewage sludge, pine bark fines, and Canadian sphagnum peat moss are commonly used to amend clay soil.
Gypsum is a good source of calcium but does not improve clay soil; it is not recommended for use in many Midwestern states.
Choose one of the amendments listed above and layer it over the existing soil. Then incorporate by hand, using a spade or shovel, or with equipment such as a rototiller. Add 1 to 2 inches of amendment when preparing an area for new lawn establishment, 2 to 3 inches for annual flowerbeds, or 3 to 4 inches for vegetable and perennial gardens. Work the amendments into the native soil to a depth of 6 to 8 inches for lawn and annual flowerbeds, and to a depth of 8 to 12 inches for vegetable and perennial gardens.
