Clay soils hold too much water for the health of most plants and dry out into a hard soil that is difficult for roots to penetrate. Plants need water, but they also need air, and the roots will drown if too much water is present. Improve clay soils by the adding large amounts of fibrous organic matter. These materials will temporarily increase the pore sizes and improve drainage. Vermiculite is not a good amendment for clay soils because of its water retention.
Till the soil. Dig moist clay soils with a spading fork, breaking up clumps and removing rocks.
Amend the soil with organic material. Manure, compost and leaf mold are preferred. Use composted manure or leach fresh manure with water before using to remove excess salts.
Add 3 cubic yards of fibrous organic matter for each 1,000 square feet of soil. Good fibrous organic amendments include sphagnum peat moss, wood chips, sawdust and straw. Dig these materials in to a depth of at least 8 inches and mix thoroughly. Use a high nitrogen fertilizer when using sawdust, grass clippings or wood materials because they will compete with the plants for nitrogen.
Get a soil pH test. Clay soils that are alkaline, with a pH above 7.0, benefit from the addition of gypsum. Excessively acid soils with pH below 7.0 benefit from the use of lime. Apply at the rate recommended by the pH test.
Add additional organic materials whenever replanting.
Dig drainage ditches for areas that have flooding problems. The soil amendments recommended will only improve drainage in the uppermost layers of soil. They will not prevent flooding.