We have heavy clay soil as well, so to loosen, we add all the leaf rankings we can find. I also bag when mowing and dump that on the garden. The leaf piles in the fall are mounded up and then tilled in. Slowly, this has worked after a couple years and we have an awesome potato patch. The soil is much looser and is greatly helped by adding and tilling in organic matter. Weedseed free straw would also work. Avoid hay as it has seeds
