Mexico City, Mexico — Climb to a rooftop and scan the horizon of this metropolis, and you’re likely to see nearby rooftops or balconies with vegetable gardens.

Urban rooftop gardening is on the cusp of a boom here, sponsored by a City Hall that sees gardening as a way to alleviate poverty, provide residents with their own healthy food, and add some green to one of the world’s most populous cities.

In a program that began five years ago, Mexico City’s municipal government has given grants to 3,080 families to build gardens on their rooftops, sometimes sheltered by simple greenhouses to protect from nightly mountain chill and occasional hail. Many more families have attended urban gardening classes and struck out on their own to grow tomatoes, lettuce, chilies, scallions, guava, passion fruit, and other edibles.

"There wasn’t anything up here before," Sergio Hernandez Rodriguez said from his rooftop in the Coyoacan district, where 2-foot-tall garden beds now display an array of corn, celery, and chilies alongside aromatic herbs and lavender.

Off to the side, his wife puttered inside a greenhouse made of plastic sheeting and clear mesh and supported by a metal frame where tufts of romaine lettuce peaked out from holes in horizontal PVC tubing. "I’m hoping to grow strawberries before long," Estela Lopez said as she showed off the simple hydroponic system using a pump made for a fish tank.

The couple spends hours each day tending to their rooftop garden, building compost and nursing seedlings. The project is already paying off – literally. "I can sell to my neighbors," Lopez said. "They know it’s very clean."

Hernandez said the garden has given him new appreciation for vegetables he once detested. His wife insisted on growing radishes, he explained with a grimace. "I don’t like radishes, but these are good," he said.

Mexico City’s small-scale urban gardening project has gained momentum.

"We’ve had growth of about 30 percent a year in projects. It just keeps growing," said Armando Volterrani, a project manager with the city program.

Residents eager to test their green thumb in Mexico City, a metropolis at an average altitude of 7,300 feet with more than 20 million people, often need help to learn how to grow vegetables.

"There are different microclimates all over the city, and rainfall and altitude also vary," explained Margarita Garcia, deputy director of the city’s sustainable agriculture program.

Scattered about the city are demonstration gardens where volunteers tell visitors about the tax break they’ll receive for having vegetation on their property and answer questions about how to grow on a balcony, whether composting is essential, and when to plant.

One of the demonstration gardens is the Huerto Romita, an explosion of green behind cyclone fencing in a partially empty lot in the central Roma Norte district of the capital.

During a break from attending visitors, co-founder Carolina Lukac explained what she tries to convey to those curious about starting a garden.

"Among the benefits of harvesting in your own home is that you don’t use chemicals and the fruits and vegetables are more alive and vital. Once you pluck them, an hour later you are eating them. There’s less loss of nutrients," Lukac said.

She dismissed concerns that growing vegetables in the sometimes visibly polluted air of the capital would affect one’s health. "With a good rinsing, they are fine," Lukac said.

A specialist with City Hall agreed.

"There’s a mobile lab that belongs to the secretariat and it does tests to determine levels of heavy metals and toxic residues," said Vanessa Morales, an engineer who works with the urban farming program. "We see no problems that would affect the consumer's health."

Lukac said the vast majority of those who visit her demonstration garden are women, many of them young. "I see this do-it-yourself spirit as stronger among young people."

A sense of pride in producing crops native to Mexico throbs at another demonstration garden in the far western Cuajimalpa district, run by a retired teacher, Maricela Segura Gamez.

She walks by a carefully tended patch of calabaza squash and chilacayote squash threaded between stalks of corn. "The chilacayotes are pure Mexican, grown only in Mexico," she said.

Along one wall of her outdoor compound, she points to fruit-bearing trees. One is a capulin cherry and another is a tejocote, a fruit that is similar to a crabapple; Mexicans often eat them around the country’s Day of the Dead holiday on November 1st and on Christmas.

In her herb garden, shrubs of rosemary, dill, and thyme sprout as well as epazote, a leafy Mexican herb with a strong aroma, a mix between lemon and fennel. "Epazote is also purely Mexican. The Chinese can never imitate it," she said.

Segura has 10 chickens in her plot, and the city program encourages residents to raise small animals like rabbits or fowl if they live in certain areas.

For those residents who need help getting started and meet certain criteria, the city program offers grants of the equivalent of between $1,000 and $2,500.

"They have to agree to participate for three years. This is the minimum timeframe," Garcia, the deputy director, said. "Only a few abandon the project, and it may be because the plastic breaks on their greenhouse. They don’t want to pay to replace it."

Mexico City is far from the leader in encouraging urban agriculture in Latin America. It took cues from Havana, and receives guidance from Cuba’s National Research Institute for Tropical Agriculture. Urban garden programs also exist in Sao Paulo, Buenos Aires, and Caracas, according to Garcia.

But in some ways Mexico City has advantages. Residents can tend gardens 12 months out of the year, and a generous four-month rainy season lessens pressure on water resources. Moreover, most buildings in the city have flat rooftops.

"Many buildings are made with accessibility to the rooftop where frequently there are cages to hang and dry your clothes," Lukac said. "So those spaces that have easy access and are excellent places to grow food in Mexico City."