Between 2008 to 2009, it seemed like every architecture proposal you saw was a vertical farm, or at least had a tuft of greenery somewhere on the facade. And in the meantime, Disckson Despommier, a Columbia professor and the idea's most prominent evangelist, seemed to pop up everywhere--from The New York Times  to the Colbert Report . The appeal, aside from sheer gee-whiz factor, would be that you can farm more efficiently while eliminating transport costs.
We're overdue for a backlash. The basic argument being that we farm outside of cities, because its economical. It can't be economical to farm in cities--otherwise we'd already be doing it. QED.
As Philip Proefrock and Hank Green argue on EcoGeek:
A farmer can expect his land to be worth roughly $1 per square foot ... if it's good, fertile land. The owner of a skyscraper, on the other hand, can expect to pay more than 200 times that per square foot of his building. And that's just the cost of construction. Factor in the costs of electricity to pump water throughout the thing and keep the plants bathed in artificial sunlight all day, and you've got an inefficient mess.
Just looking at those numbers, you need two things to happen in order for vertical farms to make sense. You need the price of food to increase 100 fold over today's prices, and you need the productivity of vertical farms to increase 100 fold over traditional farms. Neither of those things will ever happen.
Treehugger has been quick to rebut this, saying basically: Sure vertical farms are pie in the sky. They were meant simply to inspire new solutions, and they already have:
I think Philip and Hank are taking themselves and the concept of vertical farms a little too seriously. There are square miles of horizontal farming on rooftops and gardens to be done in Brooklyn and even Manhattan before we get into vertical farms. And when we do, it will probably be a more sophisticated hybrid
One such hybrid that they offer was a recent video by engineering giant Arup, which envisions a green city transformation:
Meanwhile, Green and Proefrock actually back off their apparent assertion, pointing out the huge mechanized, multi-story farming facilities, on the outskirts of cities, might in fact make sense.
But frankly, I wonder if the real impact of vertical farms might even be more mundane than that. For example, Coolhunting just posted this lovely little video of two women, Britta Riley and Rebecca Bray, who have figured out to a way to design DIY window farms:
Now, I'd argue that part of the reason why small projects like these capture our imagination is the very existence of far-out ideas like vertical farms. Those crazy concepts give imaginative scale to your daily life. And that, in itself, is valuable, because it connects something mundane with something grand--and that's good for motivating people to change.
Sure, maybe the concept of vertical farms is silly--but then again if you looked back at depictions of space in the 1950s, you'd see entire cities and civilizations. We never realized those--but we did get to space. Eventually, we really did start building space stations.
And that's how technology always advances: We get the grandest visions first, but eventually, we do see those same ideas, reworked on a scale that makes sense.
*Full disclosure: Last year I did a cover story  on Dickson Despommier, in Popular Science, talking about what some of the enabling technologies might be. So maybe I'm a bit biased in favor.