USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner’s Sons, New York. Vol. 2:724. Common lilac is a perennial, deciduous shrub that grows 12 to 15 feet tall. Lilac flowers can be white,