Although a bit of a drive over to my neck of the woods, there are three that you shouldn't miss: Brookside Gardens in Wheaton is wonderful and full of plants and gardening ideas to copy. Right now they have opened their annual summer butterfly house and that alone is worth a visit. Then in Washington proper there are the National Arboretum and the U.s. Botanic Garden which are on the opposite ends of drive through and walk around, but both worth the visit.

I agree with Kim - Brookside is worth the drive!

Closer to where you live, there are Cylburn Arboretum in Baltimore, and Ladew Topiary Gardens in (I think) Monkton.

Another "worth the drive" Maryland garden is Lilypons Aquatic Gardens near Frederick. There's also a nice herb/cottage garden near Frederick, but the name escapes me right now (I visited it a few years back with some other GW folks - maybe they can remember the name!)

Longwood Gardens in Kennett Square PA is just 1.5 hours north on Route 1(Bel Air Road). One of DuPonts estates, and wonderful.

If you have the time, try to get into DC and see Dumbarton Oaks in Georgetown.

Thanks so much for the garden information! This ought to keep me busy for some time.

One I forgot to mention and you should really see it either at the end of June (lotus flower high season) or in August for the waterlilies is one of DC's hidden gems--Kenilworth Aquatic gardens

Here is a link that might be useful: Description of Kenilworth Aquatic Garden

Cecilia, I bet you're thinking of Surreybrooke Herb Farm in Middletown near Frederick. It's definitely a favorite of mine. The Frederick, Md/Harper's Ferry, WV area is certainly worth a trip. Surreybrooke and Lilypon's is more or less along the way....if you like the scenic route.

Here is a link that might be useful: Surreybrooke

Yes, that's it - Surreybrooke! Thanks for jogging my memory!