Expanded Shale

 

This lightweight gravel-like material is gray in color and has small porous holes. When added into the soil it can help retain moisture, aerate, and breakdown clay-based soil.

If you have clay soil, try putting down 3 inches of expanded shale on top of the area you are working on, and tilling it in six to eight inches deep.

Bottom Line: Expanded shale is a relatively new and unkown product that seems to be the solution we've been looking for to deal with clay soil.