Urban agriculture has sprouted like a weed in cities from San Francisco to Vancouver.

Urban gardens were once mostly small-scale outfits staffed by volunteers, but a new generation of urban farmers is kicking cultivation into high gear.

Will Allen, founder of Milwaukee-based Growing Power, said necessity is driving the success of large-scale urban gardens. People want to know that their food is fresh and healthy, and that it benefits their communities.

“The industrial food system hasn’t worked and fed the world like we said it was going to,” Allen told Healthline. “Young people look around and see people sick and family members dying of cancer, diabetes, and obesity, and they realize we have to change our ways.”

In Detroit, a plan to create a tree farm on hundreds of empty parcels of land is like taking lemons and making lemonade. A for-profit company called Hantz Farms Detroit is on the verge of closing on about 1,500 lots it is purchasing from the city for an average of $300 each.

By this time next year, maples and other hardwoods will be planted in neighborhoods where hundreds of foreclosed, often-vandalized homes were razed.

Meanwhile, crops already are growing in the poorest areas of downtown Vancouver, Canada. There, space is at premium. In one case, the city leased the top two floors of a 10-story parking structure to a company called VertiCrop, which is growing leafy vegetables at high yields and selling them in the surrounding neighborhood.

The once-full parking garage has fewer cars now that more people bicycle to work. VertiCrop’s high-tech greenhouse grows food in rows of tall, rotating trays that resemble clothes racks at the dry cleaners.

Sadhu Johnston, deputy city manager of Vancouver and the city’s so-called “green czar,” told Healthline that many cities in North America have changed their laws to make it easier to grow food in town. “Food is really the gateway drug to sustainable living. It gets people interested in health, nutrition, and local issues,” Johnston said.

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Michael Ableman, founder of Sole Food Street Farms in Vancouver, said the biggest problem urban areas face is contaminated soil. His company, which employs former drug addicts and people with mental illnesses to help grow crops, has developed ways to grow massive amounts of food in easily movable containers.

Ableman’s most recent farm has sprouted on the site of an old gas station in one of Vancouver’s poorest neighborhoods. It contains 500 fruit trees, making it the largest urban orchard on the continent.

“I’ve been involved in this movement since the early 1980s, when there weren’t many people putting the words ‘urban’ and ‘agriculture’ in the same sentence,” Ableman told Healthline. “There were challenges not only with getting people’s heads around what this looked like, a farm in the city, but from a regulatory perspective and permitting, it was very difficult.”

Some cities have provided grants or other financial incentives for urban farmers. Still, one of the things keeping Hantz Farms from growing food, as opposed to trees for wood, is that the city of Detroit won’t allow it. Michael Score, president of Hantz Farms, said he expects that will change as the trees breathe new life into blighted areas. The company is already maintaining half of the parcels it is planning to buy and has been well received by neighbors, he said.

“Right now, we need to plant crops that neighbors can live with,” Score told Healthline. “In the countryside, if you need to spray the plants, you spray the plants. If you need to use manure, you use manure. In the city, you have to account for the close proximity to neighbors.”

Having good soil is a problem, too, Score said. And growing in stand-alone containers similar to those Sole Foods uses in Vancouver is cost-prohibitive on such a large scale.

Allen says urban agriculture really does make business sense. “Non-profits can’t survive anymore on writing grants alone. It’s about developing a business model,” he said.

Growing Power operates 160 hoop houses on 25 acres of land, and the energy-efficient hoop houses are designed for maximum yields. The organization has a diverse marketing scheme, selling its food to low-income people, to the middle class at local farm stands, and to chefs at top restaurants. Everyone pays the same price, Allen said.

Growing Power also makes money by training people from communities across the country on how to bring an urban garden to their town.

“Years ago it was very hard, with all the zoning ordinances in place, but not anymore,” Allen said. “It also has been an educational process by thousands of youth organizations teaching kids about small gardens. These kids are adults now.”

He also credited First Lady Michelle Obama for going public a few years ago about her 1,200-square-foot food garden on the White House lawn.

Allen suspects that eventually urban agriculture will become as standard as the fire hydrant, and just as important for public safety. “We have to grow healthy people; otherwise, people will be sick or obese. This new food system can create thousands of jobs in hundreds of different categories. Engineers, architects, truck drivers—every profession out there is connected to food.”