curiosity

I am curious as to whether or not an entire city could be self sustained if every home or community grew their own food. and what it would take for that to happen. Is the only reason this isn't happening now because people are lazy? a little more realistically i would really like to know what kinds of local farms there are in San Diego because i am not familiar with any, furthermore how are their businesses doing and does it at all relate the the reading "fatal Harvest" Could local farmers really a test to these claims?