Invasive Species Spotlight: The Truth About Butterfly Bush
Butterfly Bush (Buddleja [or Buddleia] davidii) is a surefire attention-grabber. A common sight in our region’s gardens and landscape plantings, its fragrant conical blooms—typically festooned with fluttering butterflies and buzzing bees—are hard to miss.
Although eye-catching, hardy, and seemingly helpful to butterflies and other pollinators, Butterfly Bush is far from beneficial; in fact it’s actually an invasive species that can impair the health of our local ecosystems.
Although Butterfly Bush grows easily in our region, it is not native to North America. The Buddleja genus originated in central China and migrated across Asia and to the Americas, evolving into over 140 species as it spread. B. davidii, the most commonly cultivated species in our region, is a native of China.
Butterfly Bush is a deciduous shrub that can grow up to 15 feet high. The opposite-growing leaves, 5-10 inches long, have jagged edges. Butterfly Bush blooms from mid-summer to early fall. Flowers form drooping or upright spikes at the end of branches. The wild-origin species is white-flowered with orange or yellow centers. Varieties bred for the garden are typically purple; or they may have pink, blue, magenta, yellow or maroon blooms.
Butterfly Bush is extremely successful at reproduction, giving it a competitive advantage over native flowering shrubs. It excels at seed production and dispersal. A study at Longwood Gardens found that there were over 40,000 seeds on a single flower spike. The shrub reaches maturity quite quickly, often producing extremely lightweight, winged seeds within the first year of growth, which travel far distances by way of water or wind. The germination rate is about 80 percent or above. These seeds can remain viable for three to five years in soil, and any cut stems can sprout again.
Butterfly Bush benefits pollinators but only at one stage of their life cycle. It attracts butterflies because it provides copious nectar. However, butterflies need host plants on which to lay eggs and on which their caterpillars feed. Not a single native caterpillar eats Butterfly Bush leaves.
If Butterfly Bush were just a pretty garden shrub, it would be less of a concern. But its high reproductive success and dispersal means that Butterfly Bush replaces native shrubs outside the garden, in natural areas. It establishes in sunny, well-drained sites including fields, roadsides, woods edges, and riverbanks, where native shrubs would have grown. Those vanished native shrubs were essential food sources for caterpillars. Without caterpillars, there will be no adult butterflies. Without caterpillars, birds will not survive.
Native substitutes for Butterfly Bush
Instead of planting Butterfly Bush, select a native flowering shrub appropriate for your site that is attractive to pollinators. For sunny, open garden or landscape plantings, try Sweet Pepperbush, also called Summersweet (Clethra alnifolia) or Virginia Sweetspire (Itea virginica). For wetter soils, try Buttonbush (Cephalanthis occidentalis)—a food source for moths—or New Jersey Tea (Ceanothus americanus). You can also plant drifts of tall native perennials. Favorites of butterflies include Blazing Star (Liatris); Purple Coneflower (Echinacea purpurea); Giant Hyssop (Agastache); Joe-Pye Weed (Eutrochium) species and Milkweed (Asclepias) species. Click here to find more ideas for butterfly plantings.
Butterfly Bush can be difficult to manage once it has been established. Seedlings can be manually removed. It is possible to uproot and dig out mature specimens. The roots must be removed or they will re-sprout. Areas around the removal site should be planted with a native ground cover to prevent future seedling germination. You must dispose of any plant material completely, by burning or putting out in the garbage. Branches left on the ground can root into new shrubs.
If you already have Butterfly Bush as a planting, and do not want to remove it, you should prevent the spread out of your garden by removing old flowerheads in the fall prior to seed dispersal. Dispose of the flowerheads in a controlled manner. Do not dump clippings or flowerheads in natural areas or compost piles.
Goats can be helpful as a control method since they consume Butterfly Bush. Although grazing alone cannot entirely eradicate the weed, in tandem with another method—such as manual removal—they can be a successful control.
There have been recent introductions to the garden markets of purportedly non-invasive Butterfly Bush. These plants have been bred to not set as much seed. If you simply must have a Butterfly Bush, these varieties may be an option, but keep in mind that they don’t provide butterflies with the hosting benefits of native flowering shrubs. And history is replete with plants touted as non-invasive that turned out to be just the opposite (case in point: multiflora rose). Eco-conscious gardeners would do better to opt for the native shrubs.
Butterfly Bush (Buddleja davidii) in flower (surrounded by native wildlfowers). Photo by Leslie J. Mehrhoff, University of Connecticut, Bugwood.org