Donna, if weeds can grow your plants can too. How are the weeds looked like? Are they healthy looking? If they are, that means the soil is fertile. If the areas you want to grow plants haven't dug or gardened for so many years, of course it'll get compacted. You just have to loosen it up by digging and turning the soil. I know it's back breaking but it's rewarding too in the end. Of course it doesn't hurt to add organic matters, like manure, compost, peat moss, or pearlite, vermiculite, and so on. But as I said, if those weeds are healthy looking, the soil is fertile and you don't have too for now.