Cinder blocks are the new concrete blocks don't weight as much as older concrete blocks. I sit the blocks on a sheet of plastic on plywood, fill one hole with Quick Crete/Sack Crete. I add more rock so it will go farther, 4 shovel fulls per 80 lb bag. After that hole cures I tie the tree in the other hole. Lay the plastic on loose dirt or sand and place the blocks with trees on it. Fill the hole with the tree with concrete. This make one block weigh about the same as 2.