How to mark a centennial? At this famed California library, with a rose.

The sign says, “Ask me about roses.” So someone does.

“Could you tell me where we can see the new hybrid?” asks Jilliene Schenkel, standing under the welcome shade of a towering magnolia tree. She is here at the famed Huntington Library, Art Collections, and Botanical Gardens near Los Angeles, where a new rose has been chosen to mark the 100th anniversary of this veritable temple to the humanities.

The man in front of the sign directs her toward a sundial surrounded by a circle of brilliant yellow roses. On that hilltop spot, the main attraction is planted immediately behind the yellows.

A rose is a rose is a rose, but the new “Huntington’s 100th” is something special – 10 years in the making by Tom Carruth, the award-winning curator of this stunning rose collection. The garden, which was first created for the enjoyment of railroad builder Henry Huntington and his wife, Arabella, is distinguished today by its vast assortment of nearly 1,300 rose varieties.

The new addition blooms in clusters of creamy yellow, then adds a gentle pink to the ruffled edges as they develop. But the calling card of the 100th is the fragrance – an intense lemon aroma, with “a little touch of powder fragrance to it,” says its creator.

“It does smell lemony, and really strong! It’s wonderful,” says Malinda Muller, who joined Ms. Schenkel in a visit to the garden on a recent Sunday.

Like Ms. Schenkel, I had read about the rose and was eager to visit the Huntington. My only other visit to this former estate and its extensive collection of books, artworks, and plants was more than 30 years ago. Back then I made sure I saw “The Blue Boy,” the full-length portrait by English painter Thomas Gainsborough, and the Huntington’s impressive Japanese garden.

Now I’m living in nearby Pasadena just as this institution celebrates the August day in 1919 when the couple established a trust to share their collections with the public. For Mr. Carruth, the curator, it seemed fitting that the anniversary also include a new blossom for the rose garden that gave the Huntingtons such pleasure – and supplied their ample flower arrangements.

To search for a rose worthy of such an honor, Mr. Carruth took his crew to the commercial rose fields in Wasco, in California’s Central Valley. As they walked along a block of “well-behaved” plants, “the rose just grabbed me,” Mr. Carruth says.

To his great surprise, it turned out to be his own creation. He bred it in 2009, when he worked for the commercial grower Weeks Roses. It takes 10 to 12 years to develop a viable rose, says Mr. Carruth, and he left Weeks for the Huntington before he had a chance to see his work come to fruition. 

Mr. Carruth’s passion for “the queen of flowers” stems from his boyhood. As a kindergartner in the Texas Panhandle, he lost his heart to a pale purple beauty called Sterling Silver that grew at the home of his mother’s best friend. As an adult, he blossomed into a plant scientist who has introduced 147 rose varieties to the world and won top national awards for his creations.

Back at the “Ask me about roses” sign, volunteer rosarian Bill Morgan fields questions from under the magnolia. A dozen clipped rose blossoms line a tray on a table in front of him. Their labels hint at their characteristics, such as the pale pink Lady Emma Hamilton – an 18th-century English performer and lover to naval hero Lord Nelson whose coy portrait hangs in the Huntington’s European gallery.

The anniversary flower, whose commercial name is Life of the Party, is not in Mr. Morgan’s lineup on this day, but he regularly gets queries about it. Potted plants of the Huntington’s 100th sold out in record time at this spring’s plant sale.

One woman wants to know whether the centennial rose would do well on the coast, where “June gloom” creates cool temperatures and overcast skies. The leaves of her rose plants get all moldy. Mr. Morgan assures her this is a “vigorous” plant that does well in a lot of climates.

I pipe up with a question. Hardly a rose expert – or even a gardener – I ask whether the 100th bushes are between blooms, because buds seriously outnumber blossoms. Meanwhile, other varieties are going gangbusters, including one gorgeous peachy-pink called Jump for Joy.

As it turns out, this celebrated newcomer blooms continually, but it drops its petals more quickly than others.

The trade-off is the fragrance, explains the Huntington’s curator. That’s why long-lasting roses shipped to the United States from Ecuador for Valentine’s Day look fantastic but have no scent.

Also, the celebrity bushes by the sundial are still young, he points out, unlike the more robust surrounding varieties, which are older and more established.

“No rose is perfect,” says Mr. Carruth. But once the Huntington’s 100th gets going, “you’ll be able to walk in that circle and not put your nose to it to smell it.”