Smith's design firm, P. Allen Smith & Associates, specializes in estate master planning, garden design and installation, with projects at public institutions, private corporations, and family estates. He is a former Board Member of the Royal Oak Foundation (the American partner of England's National Trust) and has contributed to preservation efforts at Thomas Jefferson's Monticello and George Washington's Mount Vernon among other historic properties. He is a Certified Fellow of the Royal Horticultural Society and is an Honorary Member of the Garden Club of America. Smith received the Garden Club of America's 'Medal of Honor' in 2006 at the GCA's 93rd Annual Meeting Awards Dinner in Denver, Colorado.