@ tailback: The OP now says they will wait to rent a car. Surely you aren't suggesting that they SHOULD drive after landing?

Sorry ... tailSOCK.

Thank you again for the recent responses, we have already spent several weeks in New York city and did spend many happy hours at the New York Botanic Garden, the Brooklyn Botanic Garden, the Highline, Central Park and many other smaller gardens. I have written down all the places suggested and will start investigating them so I can plan our itinerary. Cycling along the Potomac will be at the top of our list as well as many of the gardens/parks suggested. America has so much to offer as each state is so different, but so far we have enjoyed every part of America we have been lucky enough to explore. This coming trip will be a combination of train, driving and cruising - can't wait!

DC has a botanic garden also and it's right in the center so easy to get to.

https://www.usbg.gov/