Michelle Obama back on book tour. How successful are first lady authors?

Michelle Obama, like every other first lady author in the 20th and 21st centuries, sells books – lots of them. Every first lady since Lady Bird Johnson has written a White House memoir.

Michelle Obama is back on the book tour circuit for her gardening tome, “American Grown." On Tuesday, about 250 people braved a soaking rain to line up outside northwest Washington’s Politics & Prose bookstore and then file through for an autograph and a few seconds of chat with the nation’s first lady.

“Buy away. It’s Mothers Day. It’s coming up,” said Mrs. Obama, to laughter from the damp crowd. They’d all purchased an “American Grown” copy as the price of their admission.

“American Grown” is a sumptuous picture book, the story of the White House garden. It came out last year and more than 175,000 copies have been printed, according to publisher Random House. It’s got recipes and stories about other gardens that have inspired Obama, including a scent garden for the visually impaired at a New York City school.

During the appearance Obama admitted that her own daughters really just like to thumb through the book’s illustrations. She added that, slowly but surely, they’ve started to read the text, as well.

“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 on their own, because there are many ways to do it,” said Obama.

She noted that if you don’t have any suitable ground you can use containers. (She didn’t add that in the Washington area that’s a particularly good idea, because the natural soil resembles ground-up clay pots.)

Yes, it’s unusual for an author to still get personal appearances after a book’s been out 12 months. Mid-list authors with sensitive coming-of-age novels usually don’t get that treatment. But Random House probably figured that with gardening season just starting, a bit more publicity could push a more “American Grown” hardcover copies out the door. Profits go to the National Park Foundation, the official charity of the national parks.

Nowadays, first ladies just have to churn out books, don’t they? “American Grown” is the first by Obama, but we bet there are more to come. Every first lady since Lady Bird Johnson has eventually written a memoir of their White House years that received a large printing and full-press publicity, according to Craig Fehrman, an author who’s been researching a book about presidential books for several years.

This does not mean that books by first ladies are a purely modern phenomenon. The first presidential spouse to see her memoirs published while she was still alive was Helen Taft, whose book came out in 1914, according to Mr. Fehrman. Edith Wilson wrote a popular book. Eleanor Roosevelt was practically a publisher unto herself – she wrote dozens of tomes, from “Courage in a Dangerous World” to “Christmas, 1940” and “It’s Up to the Women."

“In the end, what first lady memoirs may have most in common is popularity. Every such book in the 20^th and 21^st centuries has hit the best-seller lists,” wrote Fehrman in a 2010 New York Times essay on the subject.

This should not be surprising – first ladies have generally been more popular figures than their husbands, since they don’t get as involved in controversial policies.

As “American Grown” shows, memoirs aren’t the only, or even the preeminent, kind of first lady book. The Atlantic Wire has compiled a list of some of the lighter efforts, including Eleanor Roosevelt’s, “A Trip to Washington with Buddy and Betty,” written for children in 1935, and Nancy Reagan’s, “To Love a Child,” about the foster grandparents program.

And who could forget Barbara Bush’s dog books, the classic “C. Fred’s Story," written when her husband as VP, and “Millie’s Book,” written in the White House? They purported to be in the canines’ voices, as dictated to their owner.

“Between 7 and 7:08, the President and I go off to the Oval Office,” wrote Millie in describing her day. “I often sit in on the morning briefings.... I overheard the Bushes talking the other night. Some discussion about me keeping a lower profile.”

We’d have gone the other way – maybe a higher Millie profile would have eked out a reelection victory for Bush 41 in 1988.