In general I’m skeptical of the urban farming trend. Eating locally is great, but fundamentally farming is a land-intensive enterprise and thus needs to be done where land is cheap—i.e., not in the city. Where land is expensive we should want to see buildings full of human activity. Then there can be farms maybe somewhere near the city instead of dozens of miles of endless medium-intensity sprawl.
That said, urban farming does make some sense to me for a place like Detroit, which has suffered catastrophic population loss and has tons of vacant land. The upside of decline is that a place becomes cheap, which makes it a good venue for enterprises that need low costs. Urban farming fits the bill.