Per the Spring 2011 issue of The National Gardener:
Walter Scheib- White House Executive Chef during Clinton and Bush years
Nancy Clarke- former White House Floral Designer who served for 30 years under six administrations
Thomas Tidwell, chief of the U.S. Forest Service--NGC has been partners with the forest service for 50 years; the two organizations work cooperatively on such projects as Smokey Bear/Woodsy Owl and Penny Pines.
For more information on the convention program and how to sign up: Details from NGC website