How many acres of garden or farm lend will feed family of four?
Read the book “PERMACULTURE A Designers’ Manual” by Bill Mollison. It talks about exactly what you want to do. Start a small farm to support a family. The farm must raise a wide variety of products. All the products should mesh together in a harmonious fashion. For example the waste from one part of the farm should effortlessly move to another part of the farm where it will help that part of the farm flourish. This is all stated and described much more clearly by B. Mollison. As far as how much land you need. I think it may talk about that somewhere in the book, but honestly, I am not sure.
