I'm replacing our poor lawn with raised beds for perennials and shrubs. If I'm putting down raised beds of 6" depth can I put the terrific new soil right over the grass? Will grass buried under 6" of heavy organic, compost rich soil be a problem? I realize the right thing to do would be to rototill or remove the sod but I have neither the strength nor money for that option, so it's landscape fabric or leave it in place. Any thoughts?