by Mark N. McCann
The butterfly bush most often seen in the maritime Pacific Northwest is an embattled beauty. It attracts butterflies and hummingbirds, but the species has cropped up in more far-flung sites, a great distance from urban gardens. In Coos County, Oregon, one such site may have been a dumping ground for yard debris miles from the city. The butterfly bush was found to out-compete Douglas fir seedlings for sunlight in the immediate reforestation area; this prompted the Oregon State Weed Board to add Buddleja davidii to the noxious weed “B” list in 2004. The “B” designation emphasizes the regional abundance and possible economic impact of a pest species without an outright ban of its sale. (Washington State placed this same species on the Class C noxious weed list in 2005.)
Within the Northwest, some of the largest commercial growers of the butterfly bush are searching for a cultivar that is less prodigious than B. davidii. Until that plant is available for widespread distribution, it rests on the shoulders of gardeners to control this species. The cooperative efforts by nurseries is not surprising, given the effects the butterfly bush has had in Great Britain, where it is listed amongst the top twenty worst weeds.
This plant is seen often in maritime Northwest gardens due to its rapid growth, aesthetic appeal and ability to tolerate poor soils while it attracts numerous Lepidoptera species (butterflies.) The purple flowered B. davidii is the most prolific of these Chinese natives and can top fifteen feet. Because of the species’ competitive strengths—accepting compacted, disturbed or poor soil and direct sunlight—dense thickets of the bush readily colonize eroded stream banks and gravel bars, only to be swept downstream with the next major rain event.
The plant was brought into England in 1890, and after WWII, it thrived on many bomb-damaged locations in urban areas. The danger of unexploded ordinance and the priorities of rebuilding partially damaged sites at first allowed the garden escapee to spread quickly across the island nation.
This species is particularly resistant to herbicides, often requiring two treatments to kill; moreover, cutting the stems off at the base only encourages it to grow. Some success has been achieved with a “cut and paint” herbicide method. However, Rainyside.com likes to encourage less herbicide practices and more “tug and lug”—loosening the dirt around the roots, pulling it out and piling it somewhere where it can’t sprout new roots.
Keeping a butterfly bush in your garden is not a problem if you follow some simple guidelines. Deadheading before the plant can produce fruit will keep it from spreading. Disposing all cut stems into a “yard debris” pile can prevent basal rooting, or you can treat it like ivy—turning the pile periodically until all the stems are dead.
The seed bearing capabilities of the plant are awesome. A single flower head can produce 40,000 seeds while maintaining a better than 80% germination rate. The seeds remain viable for three to five years; this means great diligence is required to remove the species completely from an area.
Interestingly, B. davidii does not compete well in shade. A garden without direct sun can help keep this pest out. It is also most competitive in disturbed, compacted and poor soil. These characteristics make it a prime suspect for stream banks in areas that have increased runoff from new development.
Native species abound to substitute for the butterfly bush. Any of the native spirea can tolerate most any wet or boggy place butterfly bush can be found, with the pink Spirea douglasii the easiest to find in nurseries. Spirea will also rapidly form dense thickets with pink showy flowers.
For flowering, low-growing species in sunny locations try Oregon checker mallow (Sidalcea hendersonii), Penstemon, columbine (Aquilegia formosa) or monkey flowers (Mimulus sp..) Native shrubs for the same location are numerous, but the most attractive are Oregon mock orange (Philadelphus lewisii), blue elderberry (Sambucus mexicana—syn. S. caerulea), Ribes sanguineum, and Ceanothus species. Ceanothus is an ideal shrub for disturbed soil or after a fire has burned an area.
Native spirea attracts large numbers of butterflies, as does the stinging nettle (Urtica dioica.) For shrub-sized species, look for elderberry (Sambucus), honeysuckle (Lonicera), roses (Rosa), Cooley's hedge nettle (Stachys coolyae) and or high bush cranberry (Viburnum edule). All these shrubs attract butterflies and hummingbirds and will tolerate direct sun light.
Native trees can also be planted to attract butterflies and hummingbirds. The best choices are western crab apple (Malus fusca), dogwood (Cornus nuttallii), oak (Quercis garryana), maples (Acer circinatum and Acer macrophyllum) and hawthorne (Crataegus douglasii). Make sure you buy the Pacific Northwest native species of hawthorne, which has leaves that are not deeply lobed like other species.
Mark N. McCann is currently working on a book about Green Space and Stream Stewardship within the Vancouver-Seattle-Portland-Eugene (VSPE) Corridor. Based on his five years of experience removing invasive species, and replanting and propagating natives species within the Tryon Creek State Natural Area (TCSNA) as a member of the Adopt-A-Plot program. He has been a Citizen Member of the Tryon Creek Watershed Council, Friends of Tryon Creek and presently is a volunteer at Berry Botanic Garden, specifically in the Native Plant’s Trail and in the Propagation Department.
Photograph by Debbie Teashon