Here is what we suggest for clay soil:
One way to improve Clay Soil when planting a new lawn, trees and shrubs is to use Earl May Structure. By mixing the structure in the soil when planting, the structure will act like tiny reservoirs storing moisture, oxygen and nutrients, also releasing them to the roots when needed. The “Structure” helps reduce compact soil problems, helping the plants to grow better and be more productive.
Another way to improve clay soil is to use Earth Right Ready to Spray Soil Conditioner. Lawns treated in the spring and fall with Earth Right will be thicker, have better soil drainage. The Earth Right contains thousands of beneficial microbes required for proper plant growth and disease resistance. The Earth Right is ready to spray and requires no mixing. Simply hook to the end of a hose and spray. First-time users should apply product at a double rate.
Both of these products are available at our Garden Centers and also online at earlmay.com