If it's large enough to really be considered a farm, as opposed to a large commercial garden, it isn't urban. By definition. If there's enough agricultural land in an urban area to make even a dent in the food needs of the people in that area, it isn't an urban area.
I'm not just nitpicking here. Farming, and not just modern industrial farming, is a large scale endeavor. A few acres of plants does not qualify as a farm. It's a commercial garden. Great! Just not the same thing.
A 5 acre