As an opener, I was reading recently that vehicle fumes don't spread much past 20 metres on open ground or upwards so, assuming smog isn't a big issue where you live, eating food grown in cities should be fine past about the second storey.

It turns out - for instance looking at Mel Bartholomew's work¹ that most crops and garden flowers don't need more than six inches deep of rich soil to do well. He claims that a four-foot (120cm) square box will produce enough salads to keep a person or two going for a full growing season and that three boxes should produce most of the veg and salads a person needs. If the soil isn't loam based, so it's light and water absorbent it's not going to be all that heavy (good for roof gardens). He's very insistent about his soil mix, but I've taken to using growing bag mixture which I'll feed with compost when I change crops. It's working well for me so far.

The main value of his stuff is that he splits the beds into 30cm x 30cm (1ft x 1ft) square, marked with (in my case) bamboos laid on the soil. A different crop generally goes into each, moving around all the time. The extra constraint of planting crops into those small spaces is really helpful in making planting decisions as you go along. The boxes are big enough to hold moisture and provide a living soil for the plants and watering is much easier than multiple containers, which I can never manage to keep properly watered.

Shrubs and trees obviously need different treatment, but they have to live in bigger, deeper containers that are big enough to hold enough moisture anyway.

Continue doing this for about 4 tyres more and depending on the species you should end up with about 25 pounds of potatos for the use of very little space.

Interviewer: What do you believe is behind this recent increase in terrorist bombings? Helpmann: Bad sportsmanship

This past April I put 30 home made versions of an Earthbox on my flat garage roof.  I live in a relatively dense urban environment (Chicago), container gardening is the only way to go.  The Earthbox - http://www.earthbox.com/ - has a water reservoir, only needs fertilizing once, no weeding or mulching.  It's been quite an adventure; bugs, mold, mildew.......  

I'm trying to get the photos on a flicker page.  In the meantime, here's a couple links.

Homemade earthbox - http://www.josho.com/Earthbox.htm

Also, the City of Montreal has a rooftop gardening program - http://rooftopgardens.ca/en?PHPSESSID=ead547e5df9625f40e148fff6e36f8ef

Here's a good one in Chicago that I just found - http://www.urbanhabitatchicago.org/projects/true-nature-foods/

In my realm, I'm teased by neighbors about the grape vines I have growing in the common courtyard. When will we be tasting Château Leofing?, they ask. Weell, that may take time, but in the meanwhile the red grapes I produce are very tasty. With cheese, they're heaven.  

Sage, rosemary, basil, thyme, chives, chervil do well in pots, here; tomatoes and strawberries, too. This year's experiment is a Cassis bush, which is going great guns, and I have a new cherished little fig tree.

Many don't realize how much can be done, with as small a space as a window sill, to courtyards, to full-fledged gardens and roof-tops ...

Gardening is great in itself, but it's the best thing ever when one is short on ideas and in need of a creative breather.

At 9 a.m. on a cool, bright Saturday in mid-June, Robert Burns and Diana Baldelomar set up a farm stand outside the YMCA in Boston's Dorchester neighborhood. The stand is simple: a tent to keep out the sun, two folding tables set in an L-shape and a handful of zinc washtubs filled with two inches of water. In the tubs stand heads of green and red lettuce, greens, broccoli, and bunches of mint and basil.

    When two women approach and ask the price of the greens, Baldelomar tells them that the turnip, mustard and collard greens are a dollar a bunch. "Honey," the woman says, "in this neighborhood, if someone asks you for greens, they are only talking about the collards." Her companion asks, "Did you ship it in from the country?"

    "No ma'am. These are from right around the corner, West Cottage and Brook. We went out and harvested them this morning. You should stop by sometime."

    Burns and Baldelomar work with the Food Project, a community-based urban agriculture program founded in 1991 to get Boston's youth involved in food production. Their West Cottage plot is one of four farms on vacant lots in the Dorchester neighborhood.

    The Food Project is part of a growing urban agriculture movement to improve access to quality food in cities by creating local sources of fresh produce. The movement is showing that sustainable, local food systems are not only a way to ensure food security but also a means of addressing social justice issues.

[lots more, worth a read]

I have used Earthboxes and they are actually a treat for patio and limited-space container garden projects.  Low maintenance, the average adult can drag one around even after it is filled and growing, and the reservoir is a godsend in hot dry climates.  Lots of folks make similar wicking-reservoir planters these days.

Next comment is that excellent soil can be made by keeping a few worm bins about the place:  food scraps, yard waste, and humanure can all be converted by redworms (or Hermetia larvae) and patience into excellent nutrients to mix with whatever nice absorbent fibre/carbon you have lying about.  And then you can also experiment with Tierra Preta techniques on a small scale if inspired.

My last comment is that this is exactly the kind of dense small scale polyculture that has sustained humanity for millennia, very efficiently and deliciously, and which monocrop feudalism -- of which corporate agriculture is only the latest flavour -- tries to stamp out wherever it, so to speak, crops up.

Good book of the week:  Carlo Petrini's latest (I think -- he's a prolific fella), Slow Food Nation -- lousy title, obviously intended to ride on the coat tails of Fast Food Nation, a cheap and demeaning  trick of the US publisher.  If I'd published it I would have called it "Good, Clean, and Fair" which is CP's theme throughout:  that a human right should be access to food that is good (tasty/delicious/nutritious/fresh), clean (not poisoned or contaminated, not produced by biosphericidal methods), and fair (not produced by slavery, peonage, conquest, theft etc).

as he points out, coming at it from many angles through many anecdotes and much background, good/clean/fair add up to "local" for the vast majority of foodstuffs, though like most reasonable folk he leaves some room for long haul trade in surpluses of attractive high-value foodstuffs, after local needs have been met.  the english translation is a bit clunky at times and makes me wish I could read the original Italian which I'm sure is more graceful, but it's a good book nonetheless -- bridging the gap between the foodies and the landless rights movements, the four star chefs and the K-12 school garden.

oh yeah, google also for Guerrilla Gardening and some really interesting links will come up.

must... sleep... must... sleep... must... sleep...

The difference between theory and practise in practise ...

The garden he built up there was laid atop a very solid structure over the garage, a building that could support a high rise, built with rebar every 6 inches (it had to support multiple firetrucks). Many, many tons of sod were laid over a strong rubber lining on the flat roof. For a decade, flowers and vegetables grew, and low and behold a tree! Unfortunately, roots are strong and they dug through the rubber coat and created a permanent leak in the roof of the structure.

How to remove all that sod then and repair the leak?

The problem cost almost as much as the building itself.

I didn't buy.

I have pictures though of that wonderful, beautiful rooftop garden. It was amazing.

Note to self: when building a rooftop garden, keep it small.