WASHINGTON (AP) -- Michelle Obama on Tuesday returned to the business of selling her first book, and she started by telling scores of people waiting in line at a popular bookstore to "buy away" because Mother's Day is coming.

"It's a great gift," she said of "American Grown: The Story of the White House Kitchen Garden and Gardens Across America."

The book was published about a year ago in late May, and the first lady did just one book-signing event in Washington about two weeks afterward. She was, at the time, taking part in an even bigger sales job: campaigning around the country to help President Barack Obama win a second term.

"If you recall, when the book came out we were in the middle of this campaign, or something or other," she joked Tuesday. "So we were a little busy."

With the election over and a second term in the history books, Mrs. Obama ventured a few miles north of the White House to the Politics and Prose bookstore on a rainy morning to plug the fruit of her first turn as a best-selling author.

More than 175,000 copies have been printed, according to Crown Publishers, which does not release sales figures.

The first lady said she wrote the 271-page book for a bumper crop of reasons: to tell the story of her White House garden on the South Lawn, to spread the word about the history of community gardening in the United States and to start a conversation about childhood obesity in the U.S.

"So all of that is part of this book, and it's trying to do a little bit of everything," she said

The book includes numerous behind-the-scenes photos, including of family dog Bo, and recipes from White House chefs.

Mrs. Obama said she hopes people who get a copy of the book will follow the example of her daughters, Malia and Sasha. She said her girls would thumb through the pages just to look at the pictures but then "slowly but surely" they started to read it. "And that's really the hope, that the pictures draw people of all ages in and then they start to read it and maybe start thinking about how to start a garden of their own," she said.

The first lady, who paired a black, short-sleeved top with silver appliques at the neckline and shoulders with a green-and-gold, pleated skirt, sat at a table covered with a blue-and-white checkered cloth and decorated with a wicker basket that overflowed with red and yellow peppers, carrots and other veggies.

Using a black Sharpie marker, Mrs. Obama spent about 90 minutes signing just her name in about 265 books, according to the publisher. Reporters were escorted from the bookstore about 15 minutes into the event.

Customers were required to pre-order one copy only of the $30 book last week, then return Tuesday morning with the receipt and a government-issued ID to receive a color-coded wristband that would allow them into the signing. They also had to pass a Secret Service background check.

Mrs. Obama shook hands with every book-buyer and chatted them up, despite admonitions by staff to the customers to "keep moving."

"It was as exciting as I thought it would be," said Marjorie Booker, a retiree in Washington, after she walked out of the store and into a driving rain after getting her book signed. "I've been looking forward to this since Thursday. The fact that I'm soaking wet is not important."

Before the signing, the first lady said all book proceeds are going to the National Park Foundation to help support the White House garden and community gardens across the country.

"So buy away. It's Mother's Day. It's coming up," she said.

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