by Peter Lesica

Invasive exotic plants pose a threat to Montana’s native grassland, woodland and riparian communities. A great deal of effort is expended controlling noxious weeds already in the state. However, the problem will never abate until we are able to prevent the introduction of new invasive exotics.  Many of our worst weeds, such as Dalmatian toadflax, purple loosestrife, tamarisk and Russian olive, got their start with the nursery-landscape trade, so it stands to reason that this industry can play a positive role in preventing future ill-advised introductions. No one wants to introduce or propagate plants that cause environmental damage or erode their neighbor’s livelihood, but how can nursery and landscape professionals identify potentially invasive plants?

Many nursery and landscape professionals are aware of the problem and are concerned about it. Articles on the subject of the nursery trade and invasive exotics have appeared in American Nurseryman, The American Gardener, and the newsletter of Lawyer Nursery, right here in Montana. More significantly, an international meeting of nursery and landscape professionals, botanists and government agencies was held at the Missouri Botanical Garden in late 2001 to address the issue. The group has released the St. Louis Declaration on Invasive Plant Species and Draft Voluntary Codes of Conduct. Craig Regelbrugge of the American Nursery and Landscape Association said the industry is committed to implementing voluntary guidelines and educating both members and consumers about the problem. Although the Codes of Conduct spell out a philosophy, they do little to spell out how a nursery professional can identify a potentially invasive species.

About the same time as the international meeting in St. Louis, the Montana Native Plant Society formed a committee of MNPS members who were also nursery and landscape professionals.  Over the course of the next year and a half this committee worked with the Montana Nursery and Landscape Association (MNLA) to develop a set of voluntary guidelines to help MNLA members choose plant materials safe for introduction. The guidelines are based on the research of many in the scientific community, most notable of whom is Sarah Reichard, a former nursery owner.  After incorporating members’ comments, the MNLA Board of Directors approved the voluntary guidelines at their meeting in May. Thanks go to Sandi Blake, Claire Dunne, Linda Iverson, Madeline Mazurski and Les Pederson of MNPS and Mary Keck, Bruce Forde and Robin Childers of MNLA for their efforts.  We believe our guidelines will allow concerned nursery professionals to make better decisions and help prevent future weed problems.

The voluntary guidelines are:

Use horticultural plants with a long history of non-invasiveness (e.g., daffodil, caragana).

Whenever possible, use plants native to North America, especially to Montana and surrounding states (e.g., mock orange, elderberry, purple coneflower, liatris).

Choose plants and cultivars that do not produce viable seed (e.g., petunia, lilac).

Avoid plants that produce prolific seeds or fruits, especially woody plants with edible fruit dispersed by animals (e.g., buckthorn, Russian olive).

Avoid plants that spread aggressively by roots or underground stems as well as seed.

Avoid plants that grow rapidly and become tall quickly.

Be cautious of exotics that originate in parts of Europe, Asia, Africa, South America and Australia with a climate similar to Montana. Know where plants originate.

Don’t use plants that are known to be invasive in Montana; it is unlawful to use plants listed as noxious by the Montana Department of Agriculture. Avoid using plants or their close relatives that are invasive elsewhere in western North America. Plant invasions start in one place first; invasive plants don’t become invasive everywhere at once.

The full text of the guidelines including introductory material, lists of noxious weeds and potential problem plants as well as the scientific underpinnings of the guidelines can be found on the MNPS website at: www.umt.edu/mnps.