The Arboretum grounds are open every day of the year except December 25 from 8:00 a.m. to 5:00 p.m. Admission is free.
What is an arboretum?
An arboretum is a living museum where trees, shrubs, and herbaceous plants are cultivated for scientific and educational purposes.
3501 New York Avenue, NE
Washington, DC 20002-1958
Tel: 202-245-2726 Fax: 202-245-4575
http://www.usna.usda.gov/Information/hoursadm.html