Alexandra Hall, 5 years old, plays in the fountains among the columns at the U.S. National Arboretum. (Linda Davidson/The Washington Post)
The Gate

It’s not easy being green. As the U.S. National Arboretum can attest, a lot of work and science goes into treating plant diseases, testing trees that can thrive in high-stress urban environments and controlling invasive plants at our borders. The arboretum, one of the world’s leading horticultural science institutions, is credited with introducing more than 700 cultivated varieties of woody and herbaceous plants into the United States. With its gardens, paths and springtime azaleas, it’s an urban oasis and Washington tradition.

2 Nonprofit groups solely dedicated to supporting the arboretum. The Friends of the National Arboretum, which began in 1949, and the National Bonsai Foundation, which began in 1982.
9 Miles of roads for visitors to walk, bike or drive. They connect 16 gardens and collections on 446 acres, including the nation’s largest herb garden, a five-acre garden of dwarf conifers and a 13-acre Asian plant collection along winding paths to the Anacostia River.

19th-century sandstone columns from the U.S. Capitol on display on a rise in the central meadow. The columns were removed from the east portico of the Capitol in 1958.

56 Azalea bonsai in the National Bonsai and Penjing Museum. These are the late-blooming satsuki azaleas, the result of hundreds of years of breeding by Japanese horticulturists. The best of these are on display from May 25 to June 2 in the Special Exhibits Wing.
1927 The year that the 69th Congress authorized the secretary of agriculture to establish and maintain a national arboretum for research and education on tree and plant life.
38,559 Minimum number of crape myrtle seeds resulting from controlled pollination by arboretum horticulturists hoping to discover disease-resistant, hardy crape myrtle hybrids.
500,000 Average visitors per year. The busiest times are spring, when the thousands of azaleas on the hillside are in bloom, and fall, when the changing leaves produce riotous colors.

Lonnae O’Neal Parker