The cherry trees, a 1912 gift from Japan, attract many visitors to the U.S. capital this time of year. The National Park Service estimates that between 400,000 and 600,000 people will visit Washington, D.C., for the National Cherry Blossom Festival during its two-week run.

Visitors come from places like Germany and Altoona, Pennsylvania, to view the spectacular trees. "Just after we announce the peak bloom date" the number of visitors to the Tidal Basin and Mall area increases, said Brian Hall, a park ranger with the National Park Service, which cares for the National Mall and the grounds of the monuments.

The National Cherry Blossom Festival is planned to coincide with the trees' peak blooming time; this year the festival runs from March 25 to April 8. Events scheduled during the festival include a parade, concerts, sporting events, a street festival, and tree planting.

Of course, nature makes the ultimate decision as to when the buds will open. The National Park Service kept track of the peak blooming time since 1921. The earliest bloom recorded was in 1990 when the Yoshino (one of the many variety of Japanese cherry trees) trees bloomed on March 15.

According to the National Park Service, April 5 is the peak bloom time this year. On this day, 70 percent of the Yoshino trees (the predominate variety around the Tidal Basin) will be in full bloom.

Today more than 3,700 cherry trees can be seen around the Tidal Basin, East Potomac Park, and on the grounds around the Washington Monument.

The two most abundant varieties of cherry trees are the Yoshino and the Kwanzan. The Yoshino typically flower on April 5, and the Kwanzan usually open on April 22. The Yoshino (Prunus x yedoensis) is a single-flowering tree, while the Kwanzan (Prunus serrulata) has double flowers.

In 1997, the park service reported that about 150 of the original trees given by Japan still remain.

To accompany the increase in visitors the National Park Service "offers new programs and additional programs," Hall said. He also noted that during the blooming season the park service schedules cherry blossom walking tours around the Tidal Basin and on the ground to the Washington Monument.

Hall said that while they increase programs and staff to assist visitors during the cherry blossom time, the park service is only at "full strength" in the summer when many families with school-age children visit the nation's capital.