If you find yourself in New York City, it is a requirement that you make it out the the Brooklyn Botanic Garden. Not a suggestion: a requirement. We went in pretty much the crappiest weather imaginable and still managed to have a great time walking the grounds. But the conservatories really made the whole trip (and the admission cost- it's only free for everyone on Tuesdays and Saturdays 10:00 A.M. to noon) worth it.
There are four different microclimates contained within beautiful greenhouse structures: Warm Weather, Tropical, Dessert, and Aquatic. For a cooler walkabout, I also suggest checking out the Bonsai Museum. While these indoor exhibitions were certainly worth our while, I would love to get the chance to visit the garden again in spring when the famed cherry blossoms are blooming.
While pretty much every single plant fascinated me, there are a few that really caught my eye. The bird of paradise flower (third from the top in the gallery below) was absolutely breathtaking. There's something about getting to see plants that you may never get to see in their native habitat that really puts things into perspective.
While I don't have much personal gardening experience to speak of, Wes has quite the green thumb. It was pretty cool to see him light up at the various species of plants. Not to mention the fact that viewing so many things that can feasibly grow outside made for a lot of future landscaping inspiration. If gardening isn't really your thing, I still got plenty of art and even fashion inspiration from the colors of the grounds and greenhouses. This is definitely one of the coolest things we did while we were in the city, so it is definitely worth adding to your itinerary.