In recent years, the Garden has become more concerned about invasive plants. In the Garden’s native habitat areas, staff members conduct research on removing invasive plants and helping to prevent recolonization. The Garden also evaluates many of the plants collected abroad through its plant exploration program before they enter the permanent plant collections throughout the Garden. The Garden’s Collection Policy states that any plant "which has the potential to threaten the genetic diversity of local native populations, overly aggressive behavior (weediness), or the ability to introduce pests or diseases will be screened and evaluated before being accepted into the collection."
Today, with an increased awareness about the environmental and economic threats posed by invasive species, the Chicago Botanic Garden is expanding and strengthening its invasive plant policy. It should be noted, however, that most exotic plants are not invasive and greatly enrich our lives. From vegetables and fruits to roses and magnolias, the best plants for local landscapes are featured in the collections of the Chicago Botanic Garden, which displays 8,900 types of plants.
1. Species known to be invasive in the Chicago region* will not be added to the Garden’s permanent collection. When species are determined to present a risk of becoming invasive, they will be removed from the collection and destroyed. The Garden will also develop, utilize and promote a list of acceptable noninvasive plants with similar landscape use as the plants being removed.
2. All species on the list of known invasive species on this website have been assigned one of two courses of action: (1) Remove – For known invasive species or cultivars, remove from Garden grounds as soon as possible and do not add to the Garden’s collection in future. (2) Phase out – For species that pose a lesser invasive risk, form significant structural features in landscape and will be costly and time-consuming to replace, phase out from the Garden over a five- to 10-year period.
For additional taxa where invasiveness is suspected but not yet understood, evaluation will take place, or taxa will be placed on a watch list for further study.
3. Interpretation about many of the species under evaluation will be provided. The list will be reviewed annually and revised as needed.
4. Besides following all laws on importation and quarantine of plant materials across political boundaries, the Garden will perform risk assessment for all plants introduced to the Garden via the plant exploration program. Species new to the United States, whether herbaceous or woody, will also be evaluated for at least four years after reaching reproductive maturity. The evaluation will follow the protocols developed by the Plant Evaluation Program and must be completed prior to the species’ inclusion in the permanent collections.
5. The Chicago Botanic Garden will not distribute plants, seeds or cuttings or other propagules of any germ plasm within its collections that is on its invasive species list or under evaluation for invasiveness. Plants that are, or would likely become, invasive in the Chicago region, or the Upper Midwest, will not be distributed via the Garden’s plant sales or the Chicagoland Grows plant introduction program.
6. The Garden will work to control invasive species in the native habitat areas, lakes and Garden grounds. Staff training in recognition and removal of invasive species will be implemented. The Garden will disseminate information about invasive species control based on its experiences.
7. The Conservation Science Department will conduct research on the biology of invasiveness and assist with the design and implementation of evaluation studies on the invasive potential of untested plant species.
8. The Ornamental Plant Development Department will evaluate the invasive potential of untested plants, and when appropriate, strive to develop noninvasive forms of known-to-be invasive landscape plants.
9. The Chicago Botanic Garden will educate the public and the nursery industry about preventing the introduction and spread of invasive species. Instructors for the School of the Chicago Botanic Garden will be asked to provide information about invasiveness, and not to recommend plants that the Garden is removing from the collections based on the issue of invasiveness.
10. The Garden will assess the threat that popular or common horticultural plants may present to related native plants in the wild. The possibility of hybridization threatening wild plant populations and their genetic integrity will be assessed. If a significant risk is present, alternatives to those horticultural plants will be sought.
*Chicago region, as defined by Swink and Wilhelm (1994) in Plants of the Chicago Region, includes the following 22 counties: Walworth, Racine, and Kenosha counties in Wisconsin; Boone, McHenry, Lake, DeKalb, Kane, DuPage, Cook, Kendall, Will Grundy and Kankakee counties in Illinois; Lake, Newton, Porter, Jasper, LaPorte, Starke and St. Joseph counties in Indiana; and Berrien County, Michigan.
Many of the policy statements are adapted from S. Reichard and P. White, 2000. Guidelines for Botanic Gardens with a Conservation Ethic. World Botanic Gardens Conservation Congress.