This is the link . In a city of museums stacked in the landscaped grid between the dome of the U.S. Capitol and the needle of the Washington Monument, federal planners of the 1920s planted the U.S. National Arboretum, a museum of trees and shrubs, in what is now a grimy section of the northeast quadrant. Stay on crowded New York Avenue and follow the signs that guide you through its curves and breaks. Or, as the distance between, say, Dogwood Circle and Rhododendron Valley is a mile and a half, you may wish to drive, following a tour route mapped out on one of the many useful fliers handed out by the arboretum. But to explore the world-famous collections of camellia, crab apple and other cultivars, you need to abandon the car and use your legs or wheelchair.
Admission is free.
Even people not horticulturally inclined have been known to spend a full day in the arboretum, oohing and aahing and pledging to build a scaled-down version of the National Herb Garden or plant a dawn redwood upon returning home. For gardeners, the arboretum is the equivalent of a vast candy store of trees and shrubs, with thousands of varieties labeled inconspicuously but fastidiously. As Department of Agriculture employees, arboretum scientists are charged with hybridizing woody plants. Their job is to produce cultivars superior to those on the market in qualities such as size and beauty of the bloom, cold hardiness and disease resistance. New trees and shrubs developed by the arboretum are displayed in its Court of Honor and given to nurseries for propagation and distribution.