Students from the school, which has had a garden since 2001, will also help plant, harvest and cook the vegetables, berries and herbs. Virtually the entire Obama family, including the president, will pull weeds, “whether they like it or not,” Mrs. Obama said with a laugh. “Now Grandma, my mom, I don’t know.” Her mother, she said, will probably sit back and say: “Isn’t that lovely. You missed a spot.”

Whether there would be a White House garden had become more than a matter of landscaping. The question had taken on political and environmental symbolism, with the Obamas lobbied for months by advocates who believe that growing more food locally, and organically, can lead to more healthful eating and reduce reliance on huge industrial farms that use more oil for transportation and chemicals for fertilizer.

Image Sam Kass, an assistant White House chef, left, and Dale Haney, the White House gardener, at the site of the new vegetable garden on the South Lawn. Credit... Stephen Crowley/The New York Times

Then, too, promoting healthful eating has become an important part of Mrs. Obama’s own agenda.

The first lady, who said that she had never had a vegetable garden, recalled that the idea for this one came from her experiences as a working mother trying to feed her daughters, Malia and Sasha, a good diet. Eating out three times a week, ordering a pizza, having a sandwich for dinner all took their toll in added weight on the girls, whose pediatrician told Mrs. Obama that she needed to be thinking about nutrition.

“He raised a flag for us,” she said, and within months the girls had lost weight.

Dan Barber, an owner of Blue Hill at Stone Barns, an organic restaurant in Pocantico Hills, N.Y., that grows many of its own ingredients, said: “The power of Michelle Obama and the garden can create a very powerful message about eating healthy and more delicious food. I don’t think it’s a stretch to say it could translate into real change.”