- The Washington Times - Wednesday, March 24, 2004

Robert DeFeo says with a chuckle that in his role as cherry blossom forecaster, he finds the trees to be “the most consistent living species in the capital,” meaning that, yes, they will bloom.

Just when is the question he and the staff at the National Park Service are expected to answer, however. The regional horticulturalist knows for a fact that the trees will not bloom before the azaleas and forsythias. He knows cold nights will slow them down and warm days will do just the opposite, either way turning the Tidal Basin and the Washington Monument grounds into a seemingly boundless cloud of pink flowers.

A gift from Japan in 1912, the capital’s cherry trees have become a tourist attraction and the focal point of the National Cherry Blossom Festival, which began in 1935. The Park Service monitors the 3,750 trees, 125 of which remain of the original gift of 3,000 trees, to count the days until the buds can be expected to bloom, an important factor for the timing of the annual festival.

Some festival-goers equate the cherry trees with the festival and are disappointed when the trees bloom before or after, which is a “shame,” Mr. DeFeo says. “The cherries don’t know the difference,” he says.

Weather conditions, not a festival date, determine when the District’s 2,763 Yoshino cherry and 11 other varieties bloom.

The festival is planned around the average recorded peak blooming date, identified as April 4, when 70 percent of the Yoshino cherry blossoms are open. This year, the Park Service predicts the peak bloom will occur between Sunday and April 10. The estimate has been pushed back a few days from earlier projections in response to recent cold nighttime temperatures. The earliest peak bloom for the Yoshino cherry since record-keeping started in 1921 was on March 15, 1990, and the latest was April 18, 1958, both caused by unseasonably warm or cool temperatures.

“They have been reliable over the years. There hasn’t been a disappointing bloom,” says Wayne Boyland, horticulturalist for Merrifield Garden Center in Merrifield. “The flowers are magnificent. They are very profuse, like a beautiful cloud.”

Each year, the Park Service monitors the Yoshino cherries, non-fruit-bearing trees, by counting the days before they can be expected to bloom based on the weather forecast and on the five stages of bud development.

The first stage occurs with the appearance of green color in the buds in late February or early March. In the second stage, florets, which are clusters of small flowers, begin to push out of each bud, becoming visible in March an average of 16 to 21 days before peak bloom. The buds break out of their protective sheaths, a waxy coating that keeps the trees in dormancy through the winter, as they begin to expand in response to light and temperature. The rate at which they expand increases with warmer temperatures, particularly if the temperatures do not vary extensively from day to night.

In the third stage, the florets push farther out of the buds an average of 12 to 17 days before peak bloom. The fourth stage involves peduncle elongation as the stems of the florets become visible an average of six to 10 days before peak bloom. The last stage comes with the appearance of puffy flowers an average of four to six days before the peak. These flowers can last four to 10 days, with the full blooming period lasting up to 10 to 14 days, according to the Park Service.

“When the temperature is starting to go up to 50 degrees, that’s when the plant is starting to break,” says Armando Lopez, garden center nursery manager for Campbell & Ferrara Nurseries in Alexandria.

Cherry trees need full sunlight and a good rich organic soil with compost materials, Mr. Lopez says. As the soil warms each spring, the tree’s roots are stimulated to take in moisture for sap, which circulates through the trunk and branches to carry nutrients to the tree’s tissues. The warmer the temperature, the faster the sap flows, causing the flowers, which are already developed but compressed inside the buds, to expand to full blossom. The petals, which are held tightly inward, angle farther out and are held with less force, becoming more susceptible to wind and rain once the flowers are open.

“With cherry trees, you’re dealing with a flower that unfolds as the [bud] swells,” says Orion Taylor, assistant manager for outdoor plants at Behnke Nurseries in Potomac.

Springlike weather in the winter with a week of temperatures in the 50-to-60-degree range can cause the buds to open prematurely and make the young flower buds susceptible to frost. In addition, temperatures above the 60s can cause the buds to accelerate their bloom time, Mr. Taylor says. The trees do not respond well to extreme hot or cold temperatures and are stimulated best by temperatures from 55 to 65 degrees, he says.

“In this climate, their flowering time is through April and May. If they start showing color before that, they are blooming too early, and they may be damaged,” he says. “There is not much that can be done for any protection on this.”

A cold snap, a late-season frost and sleet can kill the flowers and cause them to turn brown and drop from the branches. If the flowers are beginning to bloom, the exposed areas of their petals may change color so that the flowers bloom pink with brown edges.

Cherry trees can withstand overnight temperatures of 30 degrees, but cold temperatures extended into the day and the next night are “harsh,” Mr. Taylor says. Even if harsh weather strikes, not all the buds will be affected because they won’t all be at the same stage of development and they receive varying degrees of sunlight, depending on whether they are in a shaded area of the tree.

“I have never seen a full-scale wipeout of cherry blossoms that people are worried about,” Mr. DeFeo says.

Cherry trees have single blossoms with one set of petals around the center, such as the Yoshino, or double blossoms with multiple petals. The cherries produce a variety of blossom colors, including white, pink and red. The Yoshinos start out pink, but as they are exposed to the sunlight, the sun bleaches the petals to a soft pink, then to an off-white and finally a pure white by the end of their blooming season.

The foliage develops after the blossoms appear, unfurling from leaf buds located underneath the blossom buds.

“Once the flower opens, the process of the lower bud almost starts immediately,” Mr. Lopez says. “That’s why cherries bloom for such a short time.”

Mr. Lopez says cherry trees “have a point of interest throughout the year” from the spring blossoms to the summer foliage, the fall colors of bronze and red, and a “nice color in the trunk” in the winter.

Mr. Boyland likes the Yoshino cherries in particular, describing them as “one of the nicer shape of any of the cherries. They are always nice to look at even in the winter when they have no leaves on them.”

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