A question that gets asked often is 'how much garden space do I need to have if I want to feed 1 person for a year'.
According to John Jeavons, to grow a balanced vegan diet you will need:
conventional mechanized techniques: 7000 sq-ft
conventional mechanized techniques (using zero fossil fuels): 28000 sq-ft
biointensive techniques: 1000 sq-ft (food only) (4000 sq-ft more likely)

