In the shadows of the elevated tracks toward the end of the No. 3 line in East New York, Brooklyn, with an April chill still in the air, Denniston and Marlene Wilks gently pulled clusters of slender green shoots from the earth, revealing a blush of tiny red shallots at the base.

“Dennis used to keep them big, and people didn’t buy them,” Mrs. Wilks said. “They love to buy scallions.”

Growing up in rural Jamaica, the Wilkses helped their families raise crops like sugar cane, coffee and yams, and take them to market. Now, in Brooklyn, they are farmers once again, catering to their neighbors’ tastes: for scallions, for bitter melons like those from the West Indies and East Asia and for cilantro for Latin-American dinner tables.

“We never dreamed of it,” said Mr. Wilks, nor did his relatives in Jamaica. “They are totally astonished when you tell them that you farm and go to the market.”

For years, New Yorkers have grown basil, tomatoes and greens in window boxes, backyard plots and community gardens. But more and more New Yorkers like the Wilkses are raising fruits and vegetables, and not just to feed their families but to sell to people on their block.

This urban agriculture movement has grown even more vigorously elsewhere. Hundreds of farmers are at work in Detroit, Milwaukee, Oakland and other areas that, like East New York, have low-income residents, high rates of obesity and diabetes, limited sources of fresh produce and available, undeveloped land.

Local officials and nonprofit groups have been providing land, training and financial encouragement. But the impetus, in almost every case, has come from the farmers, who often till when their day jobs are done, overcoming peculiarly urban obstacles.

The Wilkses’ return to farming began in 1990 when their daughter planted a watermelon in their backyard. Before long, Mrs. Wilks, an administrator in the city’s Department of Education, was digging in the yard after work. Once their ambition outgrew their yard, she and Mr. Wilks, a city surveyor, along with other gardening neighbors, received permission to use a vacant lot across from a garment factory at the end of their block.

They cleared it of trash and tested its soil with help from GreenThumb, a Parks Department gardening program. They found traces of lead, so to ensure their food’s safety, they built raised beds of compost. (Heavy metals are common contaminants in city soil because of vehicle exhaust and remnants of old construction. Some studies have found that such ground can be cultivated as long as the pH is kept neutral.)

They wanted their crops to be organic, a commitment they shared with many other farmers in this grimy landscape. They planted some marigolds to deter squirrels; they have not had rat problems, which can plague urban gardens; and they abandoned crops, like corn, that could attract rodents. They put up fences to thwart other pests - thieves and vandals - and posted signs to let people know that this was a garden and no longer a dump.

There were also benefits to farming in the city. The Wilkses took advantage of city composting programs, trucking home decomposed leaves from the Starrett City development in Brooklyn and ZooDoo from the Bronx Zoo’s manure composting program. They got free seedlings from GreenThumb and took courses on growing and selling food from the City Farms project at the local nonprofit Just Food.

“The city really has been good to us,” Mrs. Wilks said. “All of the property we work on, it’s city property.”

The Wilkses now cultivate plots at four sites in East New York, paying as little as $2 a bed (usually 4 feet by 8 feet) in addition to modest membership fees. Last year the couple sold $3,116 in produce at a market run by the community group East New York Farms, more than any of their neighbors.

Florence Russell is looking forward to this year’s offerings. On a recent Saturday she watched from the end of Alabama Avenue as gardeners worked compost into beds at Hands and Hearts Garden, one of the sites where the Wilkses keep beds, along with 24 other growers. Fresh greens, she said, would be a welcome alternative to tough collards from the local grocery.

“This is something good happening here,” Ms. Russell said.

The city’s cultivators are a varied lot. The high school students at the Added Value community farm in Red Hook, Brooklyn, last year supplied Italian arugula, Asian greens and heirloom tomatoes to three restaurants, a community-supported agriculture buying club and two farmers’ markets.

In the South Bronx a group of gardens called La Familia Verde started a farmers’ market in 2003 to sell surpluses of herbs like papalo and the Caribbean green callaloo.

At a less established operation, the Brooklyn Rescue Mission’s Bed-Stuy Farm, mission staff members began growing produce in the vacant lot behind their food pantry in 2004, and ended up with a surplus last year. So they enlisted their teenage volunteers to run a sidewalk farm stand selling collards, tomatoes and figs; this year they plan to open a full farmers’ market.

The city’s success with urban farming will receive international attention on Saturday when, during an 11-day conference in New York, 60 delegates from the United Nations Commission on Sustainable Development are scheduled to visit Hands and Hearts, the Bed-Stuy Farm and two traditional community gardens in Brooklyn.

There was not always so much enthusiasm for city farming, though.

John Ameroso, a Cornell Cooperative Extension agent who has worked with local farmers and gardeners for 32 years, said that when he first suggested urban farm stands in the early 1990s, city environmental officials dismissed the idea. ” ‘Oh, you could never grow enough stuff with the urban markets,’ ” he said he was told. ‘ “That can’t be done. You have to have farmers.’ ”

But local officials have come around.

Holly Leicht, an associate assistant commissioner at the city’s Department of Housing Preservation and Development, helped provide two half-acre parcels of city land last year. One became Hands and Hearts and the other is in Ocean Hill-Brownsville, Brooklyn.

The Red Hook farm began in 2003 when the Parks Department gave the youth group Added Value permission to use an abandoned three-acre asphalt ball field. The group started with two raised beds, built a hoop house where it could start seeds, then laid down an acre of compost two feet deep on top of the asphalt. Last year the young farmers sold more than $25,000 in goods.

Urban agriculture has been an even larger undertaking in other cities, particularly those with weaker real estate markets and a declining population.

In Detroit, where locals refer to stretches of the city as urban prairie, food gardens are scattered through backyards, schoolyards and even more unlikely spots, including the floor of an abandoned roofless furniture factory and a vacant lot owned by a local order of Catholic friars. The number of gardens has grown to nearly 450 since the Garden Resource Program Collaborative began coordinating them in 2003.

The gardeners grow much of the food for themselves, but they have also organized a co-op, Grown in Detroit, to sell their surplus peas, onions, yams and greens. From farm stands in health center parking lots and at a prime booth in Eastern Market, the city’s chaotic maze of wholesalers and local farmers, gardeners lure customers to take their first bite of a garlic scape, or compare their young spinach with that in a Del Monte box down the aisle. Next year two and a half acres that were waist high with weeds last summer will be set aside for market-bound produce.

City Slicker Farms in West Oakland, Calif., started in 2001 with a quarter-acre garden and a farm stand selling neighborhood favorites like collards and mustard greens. It has since persuaded local elementary students to volunteer and gotten owners of five additional vacant lots to let it grow food on their land.

Some operations have figured out how to make real money.

On a fringe of Philadelphia, a nonprofit demonstration project used densely planted rows in a half-acre plot and generated $67,000 from high-value crops like lettuces, carrots and radishes.

In Milwaukee, the nonprofit Growing Power operates a one-acre farm crammed with plastic greenhouses, compost piles, do-it-yourself contraptions, tilapia tanks and pens full of hens, ducks and goats - and grossed over $220,000 last year from the sale of lettuces, winter greens, sprouts and fish to local restaurants and consumers.

One key to financial success is having customers with the wherewithal to buy your goods. In New York, Bob Lewis, the head of the city office for the state Department of Agriculture and Markets, helped make this happen by getting 21 farmers at 16 sites approved to accept checks from the Farmers’ Market Nutrition Program, a supplement to the Women, Infants and Children (WIC) and senior nutrition programs.

Sarita Daftary, the program director for East New York Farms, estimates that about 60 percent of the market’s gross revenue came from the farmers’ market checks. And by the end of this year, changes to WIC will give city residents another $14 million specifically for fresh fruits and vegetables.

But land and demand are not all that successful farmers need. They have to know how to run a business or a farm.

So Growing Power, the Milwaukee group, offers several training sessions each year, and Just Food’s City Farms project holds an annual series of workshops on running farm stands.

For more formal training there is the Center for Agroecology and Sustainable Food Systems at the University of California, Santa Cruz. Founded in 1967, the center runs a six-month course for 39 students each year on its two farms.

Patricia Allen, the center’s executive director, said roughly three-fourths of her students today were interested in urban growing.

“We’re not looking at a back-to-the-land movement in any sense,” she said.

Just ask Karen Washington. She began growing food in 1985, after a city program offering a house with a yard lured her, then a single mother of two, to the South Bronx from Harlem.

Though she works as a physical therapist, Ms. Washington always knew she had another calling. “When I was a little kid I used to watch the farm report,” she said. “I always wanted to grow and be a farmer.”

Wary of chemicals and their effect on her health, Ms. Washington was determined to farm organically. She learned how to deter pests with mild soapy sprays and marigolds, encourage natural pest killers like ladybugs, and turn food scraps into fertile compost. As her skills grew, so did her ambitions. First she helped turn a vacant lot on her block into the Garden of Happiness. Then she helped defend local gardens from developers, and later persuaded the resulting coalition, La Familia Verde, to run a farm stand and test the waters for a farmers’ market.

“It’s not about making money,” Ms. Washington said. “We’re selling so that people in our neighborhood have good quality. There’s no Whole Foods in my neighborhood.”

Like many markets that sell neighborhood produce, La Familia Verde’s has attracted upstate farmers who did not venture into these areas until the locals showed them there was a market. The professionals do not compete with the amateurs though; they sell crops like corn and apples.

All this has not quenched Ms. Washington’s agricultural ambitions. In April she took a six-month leave from her job and headed to the Center for Agroecology with two other city growers. She said she hoped to take notes and start an urban farm school in New York.

With that in place, Ms. Washington said, the possibilities could be endless.

“So that the next time we ask a kid where a tomato comes from,” she said, “he won’t have to say a supermarket. He can say, Here’s an urban farm, and here is where I’m growing that tomato that you’re talking about. How great is that?”

© 2008 The New York Times