Although not in Wilmington it is only a 15 min drive to Longwood Gardens. Beautiful flowers and plants are constantly available for your viewing pleasure. You can walk around the conservatory or explore the 1000+ acres of the old Dupont estate. Every week they rotate their flowers so there is always something to view. Originally the Duponter purchased the land because he wanted to save the trees on the property from being cut down. The family began collecting trees and plants from around the world. In the early 1900's they would hold lavash parties. Now you and your family can enjoy a day of relaxation on their grounds. Season passes are very reasonable as well as the daily rate.
http://www.longwoodgardens.org