The butterfly bush — Buddleja, or Buddleia, davidii and other species — is a butterfly magnet, with fragrant, tapered clusters of lavender, pink, yellow, or white blossoms emerging on arching branches from summer into fall. An easy to grow, rapidly developing shrub, it seems a good choice for the pollinator garden.
But it’s not. A butterfly bush is a food source for butterflies, but it is not a host plant, and understanding the difference is key to understanding why butterfly populations are declining and what gardeners can do to slow this trend.
Host plants may produce nectar, but their primary role is to support the next generation by providing butterfly larvae — the caterpillars that hatch from butterfly eggs — with the nourishment they need. At the larval stage, nourishment comes from the plant’s leaves, which the caterpillars consume to support their growth and eventual transformation (pupation) from caterpillars to adult butterflies.
The host plant-larval relationship is remarkably specific. Butterfly larvae will not eat the leaves or any other parts of the butterfly bush, and the adult monarchs and swallowtails that stop by for nectar must find host plants on which to deposit their eggs. For monarchs, that means milkweed. If host plants are not available, a critical part of the butterfly life cycle cannot be completed, and over time, populations decline.
Planting butterfly bushes plus host plants, it seems, would meet all the requirements by providing nectar plus a larval food source. But there’s another problem with butterfly bushes, and that’s their ability to spread in the wild and outcompete native shrubs.
Introduced from Asia in the early 1900s, butterfly bushes are a popular garden shrub and have been widely planted. With highly dispersible seeds, they easily escape from gardens and establish themselves in woodlands, reducing the number of native nectar and host plants, and in turn, reducing the number of butterflies. In Maryland and other Mid-Atlantic states, butterfly bushes are designated as problem plants and appear on invasive species lists.
You can compensate for the impact of the butterfly bush on native species, and support the developmental needs of butterfly larvae, by planting a mix of native nectar and host plants that bloom throughout the year: milkweed (Asclepias) for monarch butterflies, asters for the pearl crescent, spicebush for the spicebush swallowtail, dogwood and viburnum for the spring azure, and black cherry and birch for the tiger swallowtail.
This approach opens a window onto the diversity and complexity of nature and the challenge, but also possibility, of creating a more natural garden. It requires research and a bit of investment in design. Is it worth the time? It is, if it’s important to know that you’re not just attracting butterflies to your garden but helping them survive.
If you’d like to read more . . .
Adelman, Lauren. “The Joy of Butterfly Host Plants.” Lewis Ginter Botanical Garden. Jul 5th, 2017. Accessed August 29, 2021.
“Butterfly Gardening Information.” Rainscapes. Department of Environmental Protection, Montgomery County, Maryland. Accessed August 29, 2021.
“butterflybush: Buddleja davidii.” Invasive Plant Atlas of the United States. Accessed August 29, 2021.
Carignan, Christa and Debra Ricigliano. “Butterfly Bush.” University of Maryland Extension. Updated April 13, 2021. Accessed August 29, 2021.
“Creating a Wild Backyard – Bad Plants Planted by Good People.” Maryland Department of Natural Resources. Accessed August 29, 2021.
Espindola, Anahi. “What’s the deal with butterfly bushes: Good or bad for pollinators?” Maryland Grows Blog. Posted on September 14, 2020. Accessed August 29, 2021.
Landscaping with Native Plants. Maryland Native Plant Society. Accessed August 29, 2021.
Schmidt, Lillia and Susan Charkes. “Invasive Species Spotlight: The Truth about Butterfly Bush.” Conservancy Blog, Brandywine Conservancy and Museum of Art. June 7, 2020. Accessed August 29, 2021.
Schmotzer, Constance. “Avoiding Invasives: Butterfly Bush.” PennState Extension. Updated April 26, 2017. Accessed August 29, 2021.
Note: The original draft of this post was written on August 29, 2021.