It is a really interesting outcome of the property value inversion there. Historically the margins on farming have been so low that you need massive scale to even come close to achieving profitability, and the capital cost of land generally rules out anything close to a major city.
But when land is available very inexpensively, the savings in transportation can be a bigger factor.
Add in the fact that Detroit has been a food desert. Lots of young engineers moving downtown and not a single supermarket in the city until the past year.
There are thousands of empty buildings and enough raw land to fuel dozens of farms as soon as the blighted houses are torn down. What has held up farming efforts is Michigan's right to farm law which never anticipated the rise of urban farms when it was written.
my basic understanding is that a few decades of marijuana grow ops funded most of the r&d, but the breakthroughs (mostly cost) in LED lighting of the last ~5 years have made it commercially viable at dollars an ounce (to weed's tens/hundreds).
"'We will need 0.6 gallons of water to grow one head of lettuce in this process,' says Adams. 'In California and Arizona, where most lettuce in the U.S. comes from, it takes 365 gallons of water to grow a single head.'"
http://www.michigandaily.com/news/urban-farmings-growing-pop...
Shrimp anyone? http://ns.umich.edu/new/multimedia/videos/22324-u-m-student-...