MEXICO CITY -- 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 begun 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 in here 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.