Rooftop gardens have become an increasingly common feature in North American cities, as urban planners extol the benefits of more greenery in the concrete jungle.

But news of precarious growing conditions in major farming states such as Florida and California as well as awareness of the importance of "buying local" have led to greater interest in using urban rooftops to grow food.

Atop Toronto's historic Fairmont Royal York Hotel, for example, executive chef Collin Thornton cuts herbs and produce that he uses in dishes served to hotel guests.

"There's nothing more exciting than being able to [harvest] something and then put it on a plate within the hour," says Thornton.

Toronto's Royal York Hotel has a roof top garden producing fresh herbs, honey and produce. 1:38

This is but one example of urban agriculture, which has "huge" potential to supply high-quality food in cities, says Steven Peck, president and founder of Green Roofs for Healthy Cities (GRHC), an industry association in North America.

Henry Gordon-Smith, a New York-based urban agriculture consultant and creator of the Agritecture blog, says the trend reflects an appreciation of what farmers do, but also an acknowledgement that cities have a role to play in food production.

"My generation, we've become very disconnected from nature, but we don't necessarily want to go back to the rural environment," says Gordon-Smith.

"We like the city, we like the things that exist there. So what urban agriculture does is it bridges that."

More than esthetically pleasing

In recent years, cities across North America have been actively developing more green roofs, which essentially means the top of a house or building that features vegetation planted over a waterproof barrier.

The benefits of green roofs go well beyond esthetic beauty, says Peck.

Whether it's older homeowners who are downsizing from a house with a backyard garden or first-time buyers who are avid locavores, being able to offer some green space "definitely helps us on the sales floor," says a spokesman for Toronto developer Daniels Group. (Eric Foss/CBC)

He says urban roofs can decrease the effects of runoff after it rains, which can include flooding and potential contamination of the municipal water supply. According to GRHC, green roofs can retain 70 to 90 per cent of the precipitation that falls on them in summer.

As well, urban gardens purify the air by filtering out pollutants. Green roofs can also help moderate the energy needed to maintain the temperature of a building by keeping the roof warmer in the winter and cooler in the summer.

Gordon-Smith says Boston and New York are among the forerunners in urban farming. Brooklyn Grange Farms in New York has two rooftop vegetable farms, totalling 1.4 hectares.

Several years ago, the City of Toronto mandated that all new buildings must include a green roof, but there's no requirement that these spaces provide a means to grow food. One area developer, however, has become committed to providing just that.

'Thriving community garden spaces'

The Daniels Corporation, which builds condos, houses and commercial spaces in the Greater Toronto Area, is behind, among other things, the Erin Mills Backyard Farm & Market in north Toronto, which has been operating for several years on the site of a planned housing community.

This focus on urban farming began while Daniels was doing initial work on the revitalization of the declining Regent Park area in downtown Toronto in 2010.

Company president Mitchell Cohen discovered "thriving community garden spaces amongst all the disrepair and neglect," says Adam Molson, a manager who oversees many of Daniels' urban agriculture programs.

Cohen realized there was abiding interest in agriculture in even the most derelict of areas, and it inspired him to make it a greater emphasis for the corporation.

Molson says this is not only contributing to a public good, but gives Daniels a competitive advantage over other builders. A number of built and planned Daniels condominiums provide opportunities for urban farming, including the roof of the One Park Place condos in Regent Park.

Whether it's older homeowners who are downsizing from a house with a backyard garden or first-time buyers who are avid locavores, being able to offer some green space "definitely helps us on the sales floor," says Molson.

Extending the growing season

For all its benefits, rooftop farming has limitations — for one thing, urban farmers are still beholden to the climate of the city they're in, which inevitably affects how much they can grow.

In 2011, Lufa Farms constructed the first commercial rooftop greenhouse in the world, a 32,000-square-foot facility atop a building in the Montreal neighbourhood of Ahuntsic, where it cultivates greens such as Boston lettuce. (Lufa Farms)

"You get two growing seasons in California," Peck points out, "and only one in Ontario."

One way to extend the urban growing season "fairly significantly" is to build rooftop greenhouses, says Peck.

That's precisely what Lufa Farms did in Quebec.

In 2011, the company constructed the first commercial rooftop greenhouse in the world, a 32,000-square-foot facility atop a building in the Montreal neighbourhood of Ahuntsic, where it cultivates greens such as Boston lettuce and swiss chard, as well as cucumbers and peppers.

Two years later, Lufa Farms added a 43,000-square-foot rooftop greenhouse in Laval, Que., where it grows mostly tomatoes.

Victoria Shinkaruk, Lufa Farms' marketing co-ordinator, says the company now produces more than 200 metric tonnes of produce per year and its goal is "to feed people who are in the city."

Lufa Farms' distribution model shows how cities might eventually become self-sufficient.

All orders for Lufa Farms produce are placed online and the company only harvests enough to meet demand, says Shinkaruk, noting that it mitigates waste.

The company ships about 5,000 baskets of produce to individual customers and local grocery stores in Montreal every week.

A lot of produce, say from California or Florida, is harvested before it is ripe so it can survive the long journey from farm to table.

Shinkaruk says because Lufa Farms is only servicing the local area, the produce is picked ripe the day it is to be sold and then taken to its central distribution centre.

The company has partnered with a number of other local growers, who reserve sections of their greenhouses for Lufa Farms' crops and also harvest ripe fruits and vegetables daily.

It's a sign that it's possible to change the way food is grown and delivered in urban settings.

"They've adapted to our distribution system," says Shinkaruk.