Butterfly Bush
Buddleja davidii
Washington State Classification
Class B — Control Required (Designated)
It forms dense thickets, especially along river banks and gravel bars, which crowd out native plants and may alter soil nutrient concentrations.
Required control in Region 1 (all western Washington counties)
Quick Reference
Identification
Growth Habit
Butterfly bush is a deciduous shrub with arching branches that can reach 15 feet in height. The showy flower spikes are often purple, and the leaves and stems are typically hairy.
Leaves
Leaves are opposite, lance-shaped, or egg-shaped. They are up to 10 inches long and 1 to 3 inches wide. They are green to blue-gray above and whitish below due to fuzzy hairs. Leaf have either short stalks are attached directly to the stem (sessile).
Flowers
Flowers have 4 petals, and are commonly purple with an orange center, but cultivars can be pink, orange, and white. Flower spikes are upright or nodding, reaching a length between 4 to 10 inches. They are fragrant and blooming begins in mid-summer.
Fruit & Seeds
Seeds are held in brown capsules and are small and winged. Plants produce copious amounts of lightweight seed that are wind dispersed. One cultivar produces an estimated 40,000 seeds per flower head.
Impact
It forms dense thickets, especially along river banks and gravel bars, which crowd out native plants and may alter soil nutrient concentrations. This shrub is difficult to control, can produce seeds during its first year and seeds are viable 3 to 5 years.
Ecology & Spread
Habitat
While often planted in yards and gardens as an ornamental, butterfly bush can colonize disturbed areas including roadsides, abandoned railroad tracks, pastures, riverbanks, and recently logged forests. Please click here to see a county level distribution map of butterfly bush in Washington.
Spread Mechanisms
Reproduction
Plants reproduce by seed. The germination rate of several cultivars is greater than 80%, with one cultivar producing 92% viable seed. Butterfly bush can also reproduce vegetatively, as cut stems can sprout roots and grow into new plants.
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Control Methods
Mechanical
- Seedlings can be hand-picked and adult plants can be dug up. However, butterfly bush thrives in recently disturbed areas, so be aware that these methods of removing plants may actually promote the growth of new seedlings. Deadhead flower spikes before they produce seed to prevent further spread.
Cultural / Prevention
- Removal of butterfly bush is best when it first comes into flower but has not yet produced seeds. Small plants can be easily hand-pulled when the soil is moist. Remove larger bushes by cutting the plant at the base. Dig up the stump and cover it with a thick plastic bag, or mulch to prevent regeneration. Remove new shoots until the rootstock dies, and do not leave stems on the ground, or they may