The Hydrangea That Keeps On Giving

Endless Summer, a hydrangea breakthrough.
Endless Summer, a hydrangea breakthrough. (Bailey Nurseries)
By Adrian Higgins
Washington Post Staff Writer
Thursday, July 27, 2006

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.

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