yes, I think I've come to the conclusion that around 1000m² per person should be enough to have a significant impact on food supply per person in a non-optimal,

yes, I think I've come to the conclusion that around 1000m² per person should be enough to have a significant impact on food supply per person in a non-optimal, manual-labor based workflow. 1/3m² won't cut it as the mother of the preposter probably also ate a healthy dose of carbohydrates, proteins and fat which generally are not abundant in any typical "decorative" vegetables. And if you want to selfsustain your family you really need a lot (just look at the weight of military ready-made meals and think that you have to produce that (as a baseline) (x 365 x number of people supplied). Also in any urban setting, the supply of clean water will kill you faster than any lack of food.