One of the best times to make a trip to DC is when the cherry trees are blooming. Pictures do not do it justice, it is like a huge white and pink and fragrant cloud.
Prokop, the fragrance of all those cherry trees is almost intoxicating. I was Stationed in Norfolk, Va when I was in the US Navy and went to the national cherry blossom festival a couple of times. As shown on this website link, the trees (3000 of them) were donated by the mayor of Tokyo in 1912. Every spring, many thousands of folks get to enjoy that gift. It's a wonderful time.