http://www.usna.usda.gov/

You'll love the cherry blossoms around the tidal pool! Be sure to get there as early in the morning as possible if you want to park. Then walk around. As for gardens that are open to the public, I highly recommend two house/gardens in Georgetown that are close to each other: Dumbarten Oaks & Tudor House. Also, the National Arboretum is big and beautiful -- and free, but is in a fairly hard to get to location on the edge of the city. The grounds of the National Cathedral on Wisconsin Avenue just above Georgetown are beautiful, and there is a greenhouse there that sells beautiful plants and is affordable. Finally, just walking around any neighborhood in April will be a feast for the senses!

Thanks for the replies. The national arboretum site was down for several days, I finally got through. I will check out dumbarten oaks and tudor house.

I appreciate the input!

The National Botanical Gardens, on the mall between the Capitol and the Museum of the American Indian (which is an amazing place to visit, having its own interesting gardens along with my favorite restaurant of all the Smithsonian eateries), is chock full of interesting things. Bartholdy Park, behind the conservatory, is always spectacular, and the new National Garden was opened just last year. It's a little raw at this point, but still interesting.

Farther afield, Green Spring Gardens in Alexandria (about 10 minutes south of DC off 395) is a great municipal garden with a terriffic plant shop run and supplied by volunteers. Brookside Gardens in Maryland (just to the north of the city) is a similar setup - I haven't been there, but it sounds great.

Have fun!

Bubba62, thanks for the info. I will certainly be visiting some of them, and the Alexandria one sounds interesting as well. My week is filling up! Now I hope for warm walking weather :-)