The kitchen staff pickled a number of vegetables harvested from the White House kitchen garden. But were any used in the state dinner's salad course? (From the White House/First Lady of the United States)

Call it the mystery of the “winter garden salad.”

The day before Tuesday night’s state dinner honoring French President François Hollande, the White House released details of the four-course seasonal American menu, designed by executive chef Cristeta Comerford. The state dinner announcement included the sources for many of the featured ingredients, though mostly in broad terms: osetra caviar from Illinois, bittersweet chocolate from Hawaii, etc.

The exception was the second course, a winter garden salad featuring petite mixed radishes, baby carrots and merlot lettuce. The early menu described it as a “tribute to The First Lady’s White House Kitchen Garden,” an indirect nod that made sense given that vegetable gardens tend to go dormant when the ground turns cold and hard. The description did not specifically say where the ingredients were sourced.

But that same Monday, Michelle Obama tweeted a photo of countless Ball jars packed with vegetables apparently pulled from the White House kitchen garden. “Pickled veggies from the @WhiteHouse Kitchen Garden ready to be added to tomorrow night’s #StateDinner! #LetsMove,” the first lady wrote.

The next day, mere hours before the state dinner, the White House released a behind-the-scenes video.

The White House apparently keeps its kitchen garden working year round with small hoop houses. (Tim Carman/The Washington Post)

“We wanted to give our guests a taste of the kitchen garden,” Comerford tells the camera. “We were very fortunate that during the summer months, we had so [many] varieties of vegetables from the garden that we were able to pickle.”

Comerford lists a few of the vegetables available, including fennel, hot peppers and sweet onions. “We’re incorporating a lot of these pickles into some of our canapes and some of our salad.”

Calling the salad the first lady’s “signature dish,” Comerford says the plate looks more like a terrarium. The chef then mentions some of its ingredients, naming those miniature carrots and radishes, but also noting the presence of cucumbers. “And do not forget, we also have the White House honey,” Comerford says, “that we’ll be using for our dressing.”

“It’s a little representation of the kitchen garden,” she adds about the salad. “It’s really going to be an awesome plate.”

But if you compare the ingredients of the salad with the pickled vegetables available, the two lists don’t line up. So just what ingredients in the salad came from the White House kitchen garden?

Late Thursday, as another round of snow blanketed the ground, a White House official kind of, sort of cleared up the picture. The pickled ingredients were used in various canapes, and thyme, sage and rosemary from the White House kitchen garden were rolled into an herbed ricotta, an uncredited ingredient in the salad.

But that just lead to another question: Were these fresh herbs actually grown in the White House kitchen garden or some other place, like a nearby greenhouse? A White House official would confirm only that they came from the garden.

In speaking with previous White House chefs, I know the kitchen staff has been growing its own produce for decades, long before the White House kitchen garden. They typically were plants and herbs grown in pots — not on a plot of land on the South Lawn where the first lady’s garden is located.

“We had pots of tomatoes and peppers and cucumbers and herbs and stuff,” said John Moeller, a White House chef from 1992 to 2005. “But we kept it up on the roof of the White House, right outside by the window of my office, our office.”

“It was just big pots, and they were just lined up against the wall,” Moeller added.

Could those pots still be on the roof, providing the herbs in the salad’s ricotta? I’m still waiting on the White House for a precise answer on the source of the herbs. But in the meantime, I drove down to 1600 Pennsylvania Ave. to see if I could unravel the mystery myself.

That’s when I saw them on the South Lawn, right where the kitchen garden sits: tiny hoop houses, those plastic-covered structures designed to extend the growing season. They‘ve been a staple of the White House kitchen garden for several seasons now, a fact that I had all but forgotten when it was first reported years ago. In short, it seems the herbs could have indeed come from the White House kitchen garden.