The Hydrangea That Keeps On Giving
There's No Blooming Limit To Endless Summer's Virtues

By Adrian Higgins
Washington Post Staff Writer
Thursday, July 27, 2006; H01

In the past four decades, Michael Dirr has gone through untold numbers of size 13 hiking shoes in his treks through graveyards, mountain trails, college campuses and urban parks, to name a few of his haunts.

Along the way, the 62-year-old horticulture professor has amassed an encyclopedic knowledge of the vegetation that forms our living environment. Trees and shrubs may barely register in our daily lives, but Dirr is scanning them all: native, exotic, beautiful, ugly, healthy, diseased, rare, vulgar. All these traits race through his mind, but one is uppermost: Does a viburnum or dogwood or crape myrtle exhibit a quality not seen in other individuals, and can that be exploited?

Dirr, you see, thinks that a lot of garden plants are dogs. Why not find better ones? This credo has defined his career, first as the author of a standard textbook on trees and shrubs used in the landscape, "Manual of Woody Landscape Plants," now in its fifth edition, and later as a lecturer and a plant-breeding director at the University of Georgia. A big guy who talks up a storm, his following extends beyond academia into the realm of popular gardening. His slide lectures and tours are usually fully subscribed.

So his reputation would have been secure enough even if he had not happened to be in St. Paul, Minn., one September day in 1998, when he paid a visit to the trial garden of a major wholesale grower named Bailey Nurseries and discovered what may turn out to be the Holy Grail of horticulture: the foolproof hydrangea.

In a forgotten corner of the nursery, Dirr chanced upon a row of Hydrangea macrophylla with their distinctive pink mopheads. In Minnesota in late summer that could mean only one thing: The shrubs were flowering on wood that had grown that very year. Bigleaf hydrangeas aren't supposed to do this; they normally bloom from buds developed the previous year.

To Dirr, the importance of the discovery was immediately apparent: If this oddity could be developed as a garden plant, the major failings of mophead hydrangeas would be a thing of the past. Gardeners in cold winter climates would still have blooms, and gardeners in warmer states, who often see new growth zapped by a late frost, would still get blooms. And the common misstep of pruning hydrangeas to the ground in late winter would no longer deny the errant gardener a season of mopheads.

Dirr turned to his guide and said, "Do you know what you have got?" The answer was no. Peggy Anne Montgomery, a spokeswoman for Bailey Nurseries, said the plant's potential had failed to catch the notice of growers who were focused on mass-producing trees, not breeding shrubs.

The original plant had been found by nursery employee Vern Black growing in the garden of a neighbor, Dennis Bostrom. Bostrom, a retired teacher who works seasonally at the nursery, was happy to let Black take some cuttings.

Dirr took his own cuttings back to the greenhouses at the University of Georgia's horticulture department in Athens. Hydrangeas initiate flowering buds for the following year in late summer into fall, spurred by shorter days and cooler temperatures. Dirr's team subjected the cuttings to the opposite conditions: constant artificial light and nighttime temperatures a balmy 70 degrees. "We had flower buds fully expressed, and we knew we had it then."

The nursery received a plant patent and agreed to give the University of Georgia 10 cents for each plant sold. Dirr gave it a name: Endless Summer. Introduced to consumers in 2004, it has sold 3.5 million plants so far, said Montgomery, making it "the biggest woody plant introduction in American history." Its success has been bolstered by a slick marketing campaign, but in this case, Dirr says, the plant more than matches the hype.

Apart from its re-blooming quality, the shrub is resistant to powdery mildew, the bane of hydrangeas, and grows to a standard four feet high and five feet across. As with other mophead hydrangeas, the bloom color is linked to soil chemistry and will flower pink, blue or shades in between.

Another key attribute, said Paul Meyer, director of the Morris Aboretum in Philadelphia, is that it blooms now, in the dead of the mid-Atlantic summer. While most bigleaf hydrangeas produce one long-lasting floral effect, Endless Summer re-blooms continuously until frost, bolstering its value in high summer. Montgomery said you can cut fresh flowers for the table and still get blooms in the garden.

Dirr sees Endless Summer's value beyond its own ornament and as bloodstock for other re-blooming hydrangeas. Certainly its success has flushed out some other re-bloomers. Small towns in America are full of locally unique and quirky hydrangeas that are shared in the community as cuttings, said Gary Knox, a professor of horticulture at the University of Florida. "There's one here [in Quincy, Fla.] that's favored and passed around person to person," he said. "If it ever had a name it's been lost to time, and it's just known as Mrs. Blackburn's hydrangea."

Dirr has promoted re-bloomers named Penny Mac, Oak Hill and Decatur Blue. Breeders working under Dirr's direction (he is semi-retired from the university and lives in Chapel Hill, N.C.) have developed Blushing Bride, a cross between Endless Summer and a lacecap variety. The result is a mophead type, light cream in color, a slight pink or blue tint, and double flowers. Bailey Nurseries produced about 200,000 plants this year, with a full release of 2 million planned for next spring.

He is working with another company, McCorkle Nurseries, in the distribution of others, including Mini Penny. This is a dwarf re-blooming hydrangea. (As gardens get smaller, breeders have been shrinking shrubs.)

He also is developing novel varieties of other species that have always bloomed on fresh growth. Annabelle is a long-established, showy version of the native smooth hydrangea, with a large, domed, white mophead. Dirr is working on versions with stronger stems, darker leaves and a better resistance to flopping over. He has applied for patents on two in particular: one white, one pink. He also has introduced a lacecap type called Lady in Red, with florets that are pink or blue but turn a velvety red, along with the plant's foliage, in the fall.

Naturally, Dirr thinks this is a golden time for hydrangea development, echoing the period in the early 20th century when French hybridizers developed the varieties popular today.

"I don't know why anybody down the road wouldn't want to buy anything that's not a remonant group," he said, referring to the gardener's term for re-flowering.

Meyer, of the Morris Aboretum, said the American garden has far more interesting varieties of plants than just a generation ago, and "a part of it is [due to] the concerted effort of people like Michael Dirr."

Dirr recalls shooting the breeze with a nurseryman friend. "We were kicking around whether all this new stuff was worth it, and I said, 'What do your customers say?' And he said, 'Nobody comes into my store and says, what's old?' "

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