how much can cities raise for themselves?

Mr. Hemenway, hello. I read Gaia's Garden in the intern's cabin at CRMPI in February of 2010, my fingers so cold that I hated to pull them out of my armpits to turn the pages. I survived, somehow, and as a result, I'm a big fan of your work.
Here's my question:
With world population density rising, and global demands on food and water rising in response, what part or amount of that demand do you think can feasibly be met by urban agriculture, and how can large-scale implementation best be encouraged in the private sector, especially among the working class?

My question is mostly driven by my own observation that by and large, suburban and urban people tend to prefer a supermarket to a farm stand, even when they are in a rural area, and I guess it really poses another question- how do we break the habit of instant gratification?

I've got a section in "the Permaculture City" on the pros and cons of urban food growing, and I think there are a large number of factors that make it challenging. There are examples of cities that seem to have grown a large amount of their own food, such as Havana during the "special period" after the Soviet collapse, but for the most part, cities have rarely been a significant source of high-calorie foods. The traditional pattern, until the 1960s, when cheap oil and refrigeration that allowed food to be shipped long distances, was for cities to be fed by the farms surrounding them (hence the strange license plate theme for New Jersey, "The Garden State," because NJ, rural NY, and rural CT fed NYC via truck gardens until the sixties). This is an ancient and healthy pattern.

Land in cities is expensive, and food is cheap, so the economics are weighted the wrong way. Urban soils and air are often toxic, so urban food may not be that healthy. The nutrients for fertility must be imported--it's very hard to find enough land to grow compost crops or manure-producing livestock in the city proper. Most urban farms are growing vegetables, which, though nutrient dense, are low in calories (a pound of kale has 150 calories) and it's hard to find enough land to grow the grains and other high-calorie crops that we need to give us 2000 calories a day. And there are several more reasons why growing enough food to yield a full diet is very hard to do in a city. The theoretical minimum for enough land to feed one person is around 1/4 acre (not including fertility crops or manure), though in our current food system it's more like 2-4 acres. And there's just not enough open land per person in a city to do that, except in the big, post-war sprawling ones that have large peri-urban green spaces at their edges.

So although I think growing food in cities is important as a way to connect people to the land, and has many other benefits, I'm not sure that a good designer would arrive at urban land as an appropriate place to grow significant amounts of food. There are good reasons to do it, but we're kind of imposing our desires rather than arriving at a wise solution when we try to feed ourselves from within the city limits. The ancient pattern since the dawn of civilization is for cities to be fed by the rural land that surrounds them, and, as long as we've got cities, this makes sense to me.

Toby Hemenway wrote:The ancient pattern since the dawn of civilization is for cities to be fed by the rural land that surrounds them, and, as long as we've got cities, this makes sense to me.

I agree. Do you think we are moving towards a time when the pattern of shipping food long distances will decrease?

Ben, I suspect we are, as the days of cheap energy draw to a close, and the real costs of running a global economy become more apparent. But I rarely try to predict the future any more; there are just too many unknowns, variables, and short-term manipulations of markets.

Toby Hemenway wrote:Ben, I suspect we are, as the days of cheap energy draw to a close, and the real costs of running a global economy become more apparent. But I rarely try to predict the future any more; there are just too many unknowns, variables, and short-term manipulations of markets.

ISTM, that means that prudent design would not be energy dependent not even so-called renewables since renewable components must be produced by renewables and whatever will be powered by renewables must be produced by renewables. Better to have technology appropriate to declining cheap energy.

Toby Hemenway wrote:But I rarely try to predict the future any more; there are just too many unknowns, variables, and short-term manipulations of markets.

I can appreciate that. I hope you're right, as far as food production goes; the alternative is a real kerfuffle.
Thank you.