Clay soils do not allow plant roots to breathe. The clay will also hold in large amounts of moisture during heavy rainfall and cause the roots of plants to drown in the tightly compacted soil. Amendments of an organic material must be added into clay. The best time to amend heavy clay soils is in the fall, according to the Cumberland County Master Gardeners. The organic material is then left to over-winter and aid in breaking down the tightly compacted clay soil.
Add approximately a 2-inch layer of pine bark to the clay soil garden bed.
Work the material into the clay soil by running the tiller over the area until a final depth of 8 inches is achieved.
Place a 2-inch layer of leaf mold or leaves onto the garden bed area. Till the material into the clay soil. The more the clay is worked up into the organic material, the better the soil will become by spring.
Add fully digested compost to the top layer of the amended clay soil. Till the compost into the soil.
Allow the garden area to set for the winter. The material will further break down during the cold months of the season. If possible, conduct a soil test six weeks in advance of planting a garden in the amended clay soil area. The results from the soil test will give recommendations as to any additional amendments needed for the new garden space.