But subsidies for urban farming in one of the most dense, geographically constrained, pricey U.S. cities? That's insanity. "It's part of the Urban Agriculture Incentive Zones Act, a state law spearheaded by local sustainable land-use advocates and state Assemblyman Phil Ting, D-San Francisco," the article explains. "The law encourages would-be urban farmers to turn trash-covered empty parcels into gardens with the assurance they won't be forced out after putting in a lot of time and money."

That would make sense—in Detroit. Insofar as there are blighted, empty lots in San Francisco, the policy failure is building restrictions that make it too difficult to add dwelling units. As Matthew Yglesias once put it, "San Franciscans seem taken with the fact that the city, as it exists, is already the 'second-densest' large city in America. Which is true. But also a bit misleading... Brooklyn is actually twice as dense as San Francisco. San Francisco, in fact, is less densely populated than Queens. For San Francisco to be as dense as Manhattan, it would have to house 3.2 million people instead of 805,000... It's obviously not 'politically realistic' to imagine San Francisco rezoning to allow that kind of density. But uniquely among American cities, I completely believe that 3.2 million people would want to live in a hypothetical much-more-crowded version of the city if they were allowed to."

San Francisco residents tend to self-describe as cosmopolitan liberals. But as a friend in the Bay Area once put it to me, they're often reactionary conservatives when it comes to development. I am not unsympathetic to their desire to preserve such a fantastic city. But they aren't doing any favors for those who can't make rent.

The empty lot featured later in the article perfectly illustrates why this policy is ill-conceived:

To qualify, a lot must be at least one-tenth of an acre with no permanent dwellings. The property would be reassessed at the average price for irrigated farmland, currently $12,500 per acre. For a comparison, the double lot that houses the 18th and Rhode Island Garden has been valued at around $2 million - although its current assessed value is lower since Aaron Roland has owned it for 17 years. Still, after he applies for the tax reduction, his annual $6,000 tax bill will drop significantly. Roland offered use of the property to permaculture gardeners Kevin Bayuk and David Cody in 2008, who turned it into a demonstration garden that offers permaculture certification courses and hosts school groups. The garden's pathways and benches are open to the public, and volunteers harvest whatever food it produces for low-income residents. Roland gets constant requests to sell the property, which has a view of downtown, but he wants to hold on to it partly in case his children want to build a house there one day. "I also like what's going on now with it. It's this marvelous garden in the middle of the city that's growing food," he said. "Hopefully there are other people like me that eventually might want to do some development on their land but aren't in a big rush, and meanwhile want to let it be used for this kind of public purpose."

If Roland wants to hold an empty lot amid a real-estate boom and housing crisis, all to preserve the hypothetical ability of his children to build a future house, that's his right. He owns the land, after all. But subsidizing this choice is nutty. Talk of urban gardens has aesthetic appeal to the typical San Franciscan, who associates it with community gardening, "locavore" dining, and sustainability. Those things are appealing to me too, but sound environmental policy calls for adding density to urban cores, not changing land-use restrictions to discourage building. And sound economics counsels abandoning this subsidy entirely.