Canada's largest urban farm doesn't even have enough money to erect a sign explaining to passing motorists what they're seeing off Calgary's ring road.

Three years ago, the 11-acre plot was a rock-strewn field in the shadow of facilities left over from the 1988 Winter Olympics. Since then, volunteers have tilled the ground and sent all that they've pulled from the dirt to food banks.

By the standards of rural farms, it's tiny, but Grow Calgary is unprecedented for an urban non-profit. The farm so far has donated 22,000 hampers of food and with its third season looming, organizers are aiming to fill 30,000 more. They're already starting to prepare the ground for carrots, cucumbers, potatoes and tomatoes, along with dozens of other vegetables and herbs.

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On a Sunday afternoon in late March, Paul Hughes led volunteers around the bric-à-brac operation as they prepared to clean up after the winter. Grow Calgary has no salaried workers and operates with zero government funding.

Car-friendly and awash in oil money, Calgary might seem like an unlikely place for urban agriculture to find its footing in Canada. However, from his overlooked square of dirt, Mr. Hughes has plans to circle the city with gardens.

"We came here on the bus with a shovel and a pail. There was nothing here," Mr. Hughes said. "Calgary now has the opportunity to become the number one destination for urban agriculture in the world."

With chickens and beehives now allowed in New York City and rooftop farms sprawling in Montreal, interest in urban farming has flourished over the past five years. At the same time, demand for food banks has grown quickly. By the end of 2014, use of Calgary food banks was up nearly 50 per cent over five years. Demand had increased 10 per cent over the previous year's record.

Mr. Hughes submitted plans last September to Alberta's Ministry of Transportation to add 60 acres of land annually to the farm over the next decade. He says nothing like his plans for a 600-acre farm has ever been attempted elsewhere.

While Grow Calgary looks to expand, municipal officials say they have embraced urban agriculture in more crowded areas within the city. After Calgary introduced grants for new public and private gardens, the number of plots within the city has jumped to more than 200 today, from only four in 2009.

"Our vision is to create a sustainable and resilient food system for the Calgary region," said Stephanie Gagnon, a sustainability consultant for the city. "There's quite a bit of land in the city that's available."

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With a review of city bylaws under way to ensure there aren't any barriers to green thumbs, the city also has begun to plant fruit-bearing trees as it turns some parks into orchards.

Nathan McClintock, a professor at the school of urban studies at Portland State University, sees a link between the rise of urban farming and a diminishing social safety net. "With the stripping away of the welfare state, there's a growing dependence on food banks and volunteerism; people can rely less on government assistance," he said. "People are also moving back to cities and they want a back-to-the-land experience."

Lizzie Castle supervised her two young children as they helped at Grow Calgary on March 22. She had heard about the farm over the radio. "I want my kid to be involved in community things and to help out. They find it boring, but they get to run around a field and get dirty," she said. "I grew up on a farm, so I feel like this is good for them,"

More than 1,400 volunteers have helped out at Grow Calgary over the past two years.

Necessity and frugality rule on the farm. There's a motley collection of water drums and a mountain of white pails left over from stocks sent to help Calgary clean up after the 2013 floods. A steady procession of beaten-up pickup trucks drive in donations while volunteers work to drop off supplies. The entire operation relies on donations.

A greenhouse in the centre of the grounds was built from repurposed lumber and donated plastic. The entire structure cost $5 to erect – mostly spent on screws. Another structure nearby was built from tires and concrete; a third has walls made from stacks of wooden pallets.

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"This stuff doesn't cost a lot of money because we don't have any money. We've had to be creative," Mr. Hughes said. "These are the greenest structures in Calgary."