Now fill the eggshell half way up with potting soil. Add your seeds. I'm using roma tomato seeds in some of my shells and onion seeds in the rest. I like to put a few seeds in each shell because sometimes you get a dud seed and it doesn't grow. Don't put too many though or you will have to separate your plants when you put them in the ground. I might have put too many. Now cover your seeds with dirt and pack it down gently.