you might want to change the consistancy of your soil profile. That is changing it from a clayey to sandy clay loam. this would involve adding sand to allow perculation into the top 6 inches of soil. I realize that it would take a lot of sand to do this to your entire garden. That being said you could just use it in the areas you want and till accordingly. Just remember if you till the entire garden you may want to make sure that you don't mix your sandy clay with the other parts of the garden, unless you want to change your garden to a more sandy than clay substrate.