The National Arboretum in DC - fabulous, fabulous Gotelli Dwarf and Slow Growing Conifer collection. Good website with driving directions, collections and virtual tours, etc.

Huge selection of trees at The National Arboretum. There are several hundred acres of gardens right in the city. Hank

The Gotelli Conifer collection is on the far side of the Arboretum from the main gate. It can be reached from the Washington Post parking lot....at least it was possible when I was there a few years ago.

Something along the way - if you're taking I-70 across Ohio, Dawes Arboretum about 30 miles east of Columbus - Exit 132 - is worth a visit anytime of the year. Lots of conifers - both old and recent.

Here is a link that might be useful: Dawes Arboretum

Susanna Farm Nursery in Boyds Maryland specializes in conifers...great place...lots planted to view and inventory to buy. Brant Baker is the owner. They're about 35 min +/- outside of DC...details on their website

I'm not mentioning this to be snarky so please don't take offense. Sometimes people look for "landmarks" when in unfamiliar territory...

It's the Washington Times bldg. clearly visible and abutting the arboretum on New York Ave., in the NE section of DC. The Post is on 15th. St. in the NW section. :-)

If the NA is something you put on your agenda, have a good DC street map and visit the arboretum when you have plenty of daylight. The arboretum is large and serene and peaceful (and you can drive around from collection to collection if acres of walking isn't your forte), but outside the gates is an area you do not want to get lost in when the sun starts going down. It's not the postcard land of the White House, the Mall and the Smithsonian, and the Lincoln and Jefferson Memorials.

Here people used to expect to get mugged or raped inside the arboretum. I missed out on going down there when I was young because of this reputation. As an adult I have been there many times, one winter I even worked there for awhile. Have seen very little I remember except for a voyeur who would drive through and park. And I knew about him because he was pointed out to me by a long-time employee, who claimed the visitor was hoping to encounter people having sex in/near the parking or some other such thing.

Thanks Duluthinblomz4. I don't mind being corrected at all.
It was 15 years ago. The Foreign Editor gave me a ride to the subway so I could get back to Foggy Bottom where we were staying. I spent the whole day wandering around the Arboretum and wished I had way more time to see what was there.
Thanks again.
Mike

If you enjoy topiary, don't miss Ladew Gardens.

Here is a link that might be useful: http://www.ladewgardens.com/