Clay soils drain poorly and are harder to manage but can be improved by adding organic matter.
Leaves, chopped straw, compost, rotted sawdust or grass clippings can be used to improve soil structure. Apply the organic matter in the fall. In the year previous to planting, destroy all perennial weeds. Take a soil test several months in advance. If nematodes are a likely problem, submit a soil sample for a nematode assay.