Urban farming will of course definitely be coming back and Detroit is not an exception. Right now, in France, we are not really having urban farming but collective crop gardens are being developped everywhere. With the reduction in incom many people can't afford to buy vegetables and this is seen as a good option by associations and people (actually it's a good option IMO).
In T2K, Urban farming will come back fast and it will take several aspects.
The first thing that will be developped, however, will probably be animal raising: chickens, rabits and pigs. These animals don't need much and can be raised in basements and back courtyard. In addition you can feed them with garbage and corps (at least for the pigs). Just as an exemple take Paris: France made laws in the 1980's to ban urban animal raising (and you still find some around). These three animals were found in Paris until well after ww2 (as in London..., and you can add turkeys). Moreover, before ww2, the main nuisance in Paris was coming from the 500.000 roosters singing every morning at about 5:00am.
Then, farming will take place again in backyard courts and at windows probably (this might seem limited but it is already taking place, people have gardens at their windows and on balconies). Then, it will spread to public parks, first starting around zoos and farms.
Right now you still have a farm in the middle of Brussels and when I was kid, a man was raising horses two blocks away from my grand mother's place in the city of Liege. In Europe, you still have plenty of "urban farm" that can be turned back to their original purpose.
One last thing, the bee population is going down all over our countrysides but it is booming in our cities.