The Globe and Mail has a nice article on Young Urban Farmers, a "Toronto-based start-up founded last year with a mission to not only turn a healthy profit, but to also encourage sustainable practices in households across the city."
Young Urban Farmers charges for installation. They charge additional fees if the homeowner wants them to maintain the garden.
The fees are quite reasonable - full service packages start at $695 per season.
While on the topic of urban farming, I want to mention Local Dirt. It is an eBay-like website where you can find, buy and sell local food. Restaurants and others use it to source local food; local farmers use it sell product.
They have a nice tool on their homepage for finding local food, including listings of farmers markets.
Also related is the New York Times article City Slickers Take to the Crops, which covers the trend of agricurious urbanites vacationing by volunteering on farms.
We're big fans of the small farm and local food movement, a key component of the broader new localism trend.