Lilacs and butterfly bushes are staples of butterfly gardens across much of North America, but these two types of plants are not the same. Lilacs belong to the genus Syringa, while butterfly bushes hail from the Buddleja genus. These plants have many similarities, but there are distinct differences between them.
Butterfly bushes are deciduous shrubs, while the deciduous lilacs are in both shrub and tree form. Lilacs have greater cold hardiness than butterfly bushes. The latter often die to the ground in the colder U.S. Department of Agriculture Plant Hardiness Zones where they grow. Butterfly bushes grow faster than lilacs, as much as 8 feet in a single growing season, according to the University of Connecticut Plant Database. As a rule, the lilacs bloom in the middle of spring, while butterfly bushes flower in summer with some blooming until first frost.
Both of these landscaping plants attract butterflies with their showy, colorful, fragrant flowers. Both are non-native types, originating in Asia from Japan, Korea and China. Butterfly bushes and lilacs thrive in a full sun site, and both withstand pruning, especially after flowering. Both have a wide array of cultivars, with the colors of the flowers variable, depending upon the cultivar. These flowers have shades of pink, purple, maroon, white, violet, yellow and red.
Most butterfly bushes do not survive the winter in areas colder than USDA zone 5. The majority grows between zones 5 and 9, including the alternate-leaved butterfly bush (Buddleja alternifolia) and a species nicknamed summer lilac (B. davidii). Some butterfly bushes have even lower acceptance of cold, like the popcorn buddleja (B. loritica), able to handle zones 8 through 10, but none chillier. Most lilacs withstand the zone 3 climate, including the common lilac (Syringa vulgaris), Meyer lilac (S. meyerii) and the Japanese tree lilac (S. reticulata).
There is a much broader selection in terms of height of lilacs, as opposed to butterfly bushes. The lilacs in tree form grow as tall as 30 feet with some of the shrub cultivars, such as Agincourt Beauty, growing to 15 feet. Smaller forms exist as well, including Bloomerang, a dwarf hybrid measuring between 3 and 4 feet high. The largest of the butterfly bushes attain heights of 15 feet. Most are as tall as a person is or smaller, with some just 1 to 2 feet high, such as the Blue Chip cultivar.