I thought the butterfly bush was a legitimate garden plant. It is lovely, it provides shade, and we would like to keep it. Do we have to cut it down? Many of my neighbors have this plant as well. Please make an effort, on your site, to discuss the gray area of desirable garden plants that may be invasive.

Reporter
June 27, 2008, 2:13 p.m.

Hello Shyla, butterfly bush (Buddleja davidii) has been cultivated in the U.S. for over 100 years (at least decades in Oregon), but was only recently identified (1999) by the Oregon Department of Agriculture as invasive. There are several well-documented sites of invasive populations of butterfly bush in Oregon, most troubling being its colonization of some riparian areas.

Here's some information from Oregon State University extension: Butterfly bush, also known as summer lilac, Buddleia or Buddleja, is a very popular garden plant in the Pacific Northwest and other temperate regions of the world. Photos of its beautiful blossoms grace the pages of slick gardening magazines and catalogs, television programs and garden center displays. Garden writers laud the butterfly bush as a fast-growing, robust, easy-to-grow shrub that attracts a wide variety of butterflies.

But there's a dark side to this popular plant. Butterfly bush can be a very aggressive, or invasive non-native shrub that, in certain situations, can overtake native vegetation, according to horticulturists with the Oregon State University Extension Service and weed biologists with Oregon's Department of Agriculture (ODA).

In Oregon, the ODA officially classified it as a class "B" noxious weed in 2004. Its strategic plan includes efforts to eradicate butterfly bush in the wild, but not from people's yards.

James Altland, nursery crops researcher at OSU's North Willamette Research and Extension Center in Aurora, and his student Julie Ream, are studying the relative invasiveness of cultivated species of butterfly bush in Oregon.

Butterfly bush is extremely invasive in natural areas. There are serious infestations on the North Fork of the Willamette River near Oakridge and along the Coquille River near the coast. It has spread to most of the counties in western Oregon and Washington. It has been a huge problem in England, where it is one of the top 20 weeds, having overtaken large tracts of disturbed land 50 years after it was introduced from China. It is a terrible problem in New Zealand as well, especially in areas prone to frequent flooding.

In reviewing the scientific literature about the invasiveness of butterfly bush in the United Kingdom, the OSU researchers found that seed there requires a long time to develop and release from the plant. British researchers have discovered that flower heads from a previous summer do not release seed until dry weather occurs the following spring, said Altland. Practically applied, this means that if nurseries and home gardeners prune all the spent blossoms off their butterfly bushes in the fall, it is a way of controlling the release of seed from the plant.

Both OSU and ODA scientists are encouraging home gardeners to pay close attention to choosing butterfly bushes that are cultivated varieties, not the straight wild species Buddleia davidii. Only this species Buddleia davidii, not specially bred cultivars are subject to Oregon's noxious weed listing. It is most commonly seen growing wild along roadsides, in riparian areas and in forest openings.

Some cultivars have been found to produce much less seed than others. For example, a study at Longwood Gardens in southern Pennsylvania found large differences in the amount of viable seed produced by B. davidii varieties. For example, cultivars 'Summer Rose' and 'Orchid Beauty' produced 20 times fewer viable seeds than 'Potter's Purple' and 'Border Beauty'. The study also found that a single flower cluster of 'Potter's Purple' was found to produce more than 40,000 seeds. In the Longwood study, some Buddleia species and hybrids produced fewer viable seeds than B. davidii and likely have lower potential for escaping gardens and colonizing natural areas.

Because you already have butterfly bush on your property, there are ways to keep it in control.

Don't let Buddleia go to seed. Deadhead, or clip off all flower heads in the fall. Do not wait until spring.

Do not leave the clippings on the ground, as they can easily take root and create a new plant. Dispose of plants by sending away in your yard debris pickup service, where it will be ground up and composted. Or burn the branches. Whatever you do, don't dump the clippings along a roadside or along a creek or river, as these are preferred habitats for escaped butterfly bush.

Watch your property for new seedlings. Dig up and get rid of any volunteer bushes. Don't give them away to friends.

Buddleia or Buddleja are both considered correct spellings of the Latin name of the genus of the butterfly bush, according to the gardeners' encyclopedia of ornamental plants called Flora: A Gardeners Encyclopedia, published by Timber Press. The genus has about 100 species in the wild. Most grown in our region are native to Asia. Others originate from South Africa. And some are from South America. Only a few species in the genus are domesticated and garden-grown in our region.

In addition to ODA's "B" noxious weed listing, Buddleja davidii appears on the "Most Invasive" species list of the Pacific Northwest Exotic Pest Plant Council and the Native Plant Societies of Oregon and Washington. The OSU Extension Service Master Gardener Program no longer recommends it for butterfly gardens because of its invasiveness.

I also encourage you to obtain a copy of the booklet GardenSmart, a recent publication available at http://www.opb.org/programs/invasives/extras/gardensmartguide.pdf. This publication does a great job describing some of the more invasive garden plants, and excellent options you can choose in their stead. For example, page 6 of this publication provides some excellent information on butterfly bush, and two excellent non-invasive options you can plant in their stead. The optional plants have similar floral characteristics of butterfly bush, i.e., these plants will provide the shade and beautiful flowers you desire in butterfly bush, but will not spread and become invasive.

The Oregon Department of Agriculture also provides some information on butterfly bush on their website at http://www.oregon.gov/ODA/PLANT/WEEDS/profile_butteflybush.shtml.

I hope this information is helpful, and thank you very much for your report.

Lisa DeBruyckere
June 28, 2008, 12:47 p.m.