My soil is mostly clay. An inch or so below that is shale. I believe I can amend the clay soil with gypsum, but I'm not sure what to do about the shale. Does gypsum work on that as well? Since shale is like rock, does this improve drainage or make it worse?
Certified GKH Gardening Expert
I think that I would add a little more than just gypsum. This mix will be a recipe for a thick mud that will eventually resemble concrete. Make sure that you add topsoil, compost, straw, and other materials that improve drainage as well. Tilling in worm castings, or introducing worms to spots that you have dug up will help with natural soil aeration.
These articles will help: https://www.gardeningknowhow.com/special/organic/how-to-easily-improve-your-clay-soil.htm