The National Arboretum in Washington, D.C. consists of 446 acres. Activities are concerned primarily with educating the public and conducting research on trees and shrubs. Research on woody plants emphasizes the development of superior forms that will grow in various climatic zones in the United States. A herbarium containing 500,000 dried plants is maintained for technical reference.

The Arboretum was established by an act of Congress on March 4, 1927. In 1973, the National Arboretum was placed on the The National Register of Historic Places.

The plantings are arranged in different combinations throughout the Arboretum. Nine miles of paved roads provide access to the principal plant groups. There are single-genus groupings of hollies (Ilex), crabapples (Malus), magnolias (Magnolia), boxwoods (Buxus), cherries (Prunus), irises (Iris), daylilies (Hemerocallis), peonies (Paeonia), viburnum (Viburnum), rhododendrons (Rhododendron) and maple (Acer).

Plant groups of unusual interest include the azalea plantings, which are among the most extensive in the Nation; aquatic plants; the National Bonsai Collection; the collection of oriental plants in the Cryptomeria Valley of the Garden Club of America; the Gotelli Dwarf Conifer Collection, the dogwood plantings of the Woman's National Farm and Garden Association; Fern Valley, sponsored by the National Capital Area Federation of Garden Clubs and other organizations; and the National Herb Garden, sponsored by The Herb Society of America. The National Bonsai Collection, a bicentennial gift from the Japanese people, is housed in a specially constructed pavilion.