Trying to amend hard pack clay is impossible. I tried to amend the soil and it would just turn back into the same hard pack by the next season. I ended up buying top soil or mushroom compost by the dump truck load. And built up the soil over the clay about 6 to 8" . Then planted tons of plants. That was 20 years ago and the garden is 21/2 acres. It worked well for my garden .
Good luck.
