“The Workshop on Linking Ecology and Horticulture


 Prevent Plant Invasions”


December 2001

St. Louis, Missouri







In December 2001, experts from across the globe met in St. Louis, Missouri to explore and develop workable voluntary approaches for reducing the introduction and spread of non-native invasive plants, which are serious threats to protecting biodiversity and ecosystems in the United States and other countries. The Workshop on Linking Ecology and Horticulture to Prevent Plant Invasions was convened by the Missouri Botanical Garden and the Royal Botanic Gardens, Kew; and brought together some of the most respected leaders in their fields for the first time (see attached list). [1]


This landmark three-day gathering yielded the Saint Louis Declaration, which consists of two major components:


1.       Overarching Findings and Principles that frame the invasive species problem and present the underlying basis for successful efforts to address it; and,


2.        Draft Voluntary Codes of Conduct that help govern decisions made by commercial, professional and government groups whose actions affect the spread of invasive plant species including government agencies, nursery professionals, the gardening public, landscape architects and botanic gardens and arboreta.


The draft voluntary codes offer professional codes of conduct designed to curb the use and distribution of invasive plant species through self-governance and self-regulation by the groups concerned. This approach has been used successfully to ameliorate other problems but its application to invasive plant threats is novel and innovative.  Importantly, the draft Voluntary Codes of Conduct were developed recognizing that education must accompany all efforts to address the problem and that some future government regulation may perhaps be needed if such efforts prove insufficient. These codes, which are attached, are now being considered for endorsement by the major professional societies and organizations representing each of the groups covered.  If endorsed they will be ‘tested’ and revised as necessary to improve their utility and effectiveness.



Workshop participants also discussed key topics and activities that drive concerns about invasive plant species worldwide. Among them were:


·         Economic and environmental impacts presented by the spread of invasive plants

·         How horticulture contributes to the spread of invasive plants

·         The nursery industry’s view of the problem and its efforts to respond to it

·         Government responses to concerns about invasive plants (the focus here was on US Government response with selected examples of how Australia, South Africa and Britain have responded in different ways)

·         Risk assessment and how it can be used to evaluate whether a new plant species proposed for introduction is likely to become an invasive pest

·         Educational tools available for helping the public become more aware of the problem

·         Plant species that might be acceptable alternatives to those invasive plants identified as harmful


Proceedings and plans for additional activities by the “Workshop Linking Ecology and Horticulture to Prevent Plant Invasions” will be released in late March. You are encouraged to direct any questions or comments to invasivespecies@mobot.org. Thank you for your interest.


The St. Louis Declaration On Invasive Plant Species

A Product of:

“The Workshop on Linking Ecology and Horticulture To

Prevent Plant Invasions”




February 2002


People are major dispersers of plants.  The magnitude of this dispersal is unprecedented and has allowed dispersal of species that manifest aggressive traits in new areas. 


Plant introduction and improvement are the foundation of modern agriculture and horticulture, yielding diversity to our supply of plants used for food, forestry, landscapes and gardens, medicinal and other purposes. 


A small proportion of introduced plant species become invasive and cause unwanted impacts to natural systems and biological diversity as well as economies, recreation, and health. 


Plant species can be invasive in some regions, but not in others.  The impacts of invasive plant species can occur at times and places far removed from the site of introduction. 


Principles (a.k.a. The St. Louis Six)

1.       Plant introduction should be pursued in a manner that both acknowledges and minimizes unintended harm.


2.       Efforts to address invasive plant species prevention and management should be implemented consistent with national goals or standards, while considering regional differences to the fullest extent possible. 


3.       Prevention and early detection are the most cost effective techniques that can be used against invasive plants. 


4.       Research, public education and professional training are essential to more fully understanding the invasive plant issue and positively affecting consumer demand, proper plant use, development of non-invasive alternatives, and other solutions. 


5.       Individuals from many fields must come together to undertake a broad-based and collaborative effort to address the challenge, including leaders in horticulture, retail and wholesale nurseries, weed science, ecology, conservation groups, botanical gardens, garden clubs, garden writers, educational institutions, landscape architects, foundations and government. 


6.       A successful invasive plant species strategy will make use of all available tools including voluntary codes of conduct, best management practices, and appropriate regulation.  Codes of conduct for specific communities of interest are an essential first step in that they encourage voluntary initiative, foster information exchange, and minimize the expense of regulation. 


 Voluntary Codes of Conduct

For Government

February 2002


1.       Require risk assessment for government-led or financed plant introductions to ensure that no new harmful plant species are introduced, intentionally or unintentionally.


2.       Do not distribute existing holdings of invasive plant species to areas where they can potentially do harm; eliminate these holdings or maintain new or existing holdings using appropriate safeguards.


3.       Coordinate and facilitate collaboration in databases, early warning systems, monitoring, and other means of preventing invasive plant species problems.


4.       Lead and fund (subject to budgetary considerations) the development of environmentally sound methods to control harmful invasive plant species, seek control of such species on public lands and promote their control on adjacent private lands.


5.       Develop and promote the use of non-invasive plant species within all government units and to the public.


6.       Facilitate, lead, coordinate and evaluate public outreach and education on harmful invasive plant species.


7.       Encourage that employees and management participate in ongoing training programs on invasive plant species.


8.       Foster international cooperation to minimize the risk of the import and export of potentially invasive plant species.


9.       Develop partnerships and incentive programs to lessen the impact of invasive plant species and provide non-invasive restoration materials.


10.   Provide a forum for regular evaluation of the effectiveness of these voluntary codes of conduct towards preventing the invasive plant species problem.


11.   Enforce invasive plant species legislation at all levels.



 Voluntary Codes of Conduct

For Nursery Professionals

February 2002



  1. Ensure that invasive potential is assessed prior to introducing and marketing plant species new to North America. Invasive potential should be assessed by the introducer or qualified experts using emerging risk assessment methods that consider plant characteristics and prior observations or experience with the plant elsewhere in the world. Additional insights may be gained through extensive monitoring on the nursery site prior to further distribution.


  1. Work with regional experts and stakeholders to determine which species in your region are either currently invasive or will become invasive. Identify plants that could be suitable alternatives in your region.


  1. Develop and promote alternative plant material through plant selection and breeding.


  1. Phase out existing stocks of invasive species in your region.


  1. Follow all laws on importation and quarantine of plant materials across political boundaries.


  1. Encourage customers to use, and garden writers to promote, non-invasive plants.


Voluntary Codes of Conduct

 For The Gardening Public

February 2002


  1. Ask for only non-invasive species when you acquire plants.   Plant only environmentally safe species in your gardens. Work towards and promote new landscape design that is friendly to regional ecosystems.


  1. Seek information on which species are invasive in your area.  Sources could include botanical gardens, horticulturists, conservationists, and government agencies.  Remove invasive species from your land and replace them with non-invasive species suited to your site and needs.


  1. Do not trade plants with other gardeners if you know they are species with invasive characteristics.


  1. Request that botanical gardens and nurseries promote, display and sell only non-invasive species.


  1. Help educate your community and other gardeners in your area through personal contact, and in such settings as garden clubs and other civic groups.


  1. Ask garden writers and other media to emphasize the problem of invasive species and provide information.  Request that garden writers promote only non-invasive species.


  1. Invite speakers knowledgeable on the invasive species issue to speak to garden clubs, master gardeners, schools and other community groups.


  1. Seek the best information on control of invasive plant species and organize neighborhood work groups to remove invasive plant species under the guidance of knowledgeable professionals.


  1. Volunteer at botanical gardens and natural areas to assist ongoing efforts to diminish the threat of invasive plants.


  1. Participate in early warning systems by reporting invasive species you observe in your area.  Determine which group or agency should be responsible for reports emanating from your area.  If no 800 number exists for such reporting, request that one be established, citing the need for a clearinghouse with an 800 number and website links to information about invasive plant species.


  1. Assist garden clubs to create policies regarding the use of invasive species not only in horticulture, but in activities such as flower shows.  Urge florists and others to eliminate the use of invasive plant material.


Voluntary Codes of Conduct

For Landscape Architects

February 2002




1. Seek out education and information on invasive species issues:

a.   Work with local plant ecologists, horticulturists, nurseries, botanic gardens, conservation organizations and others to determine what species in your region either are currently highly invasive or show aggressive potential. Investigate species under consideration that may present a threat.

b.   Increase interaction with other professionals and non-professionals to identify alternative plant material and other solutions to problems caused by harmful invasive plants.

c.   Take advantage of continuing education opportunities to learn more about invasive species issues.


2.   Identify and specify non-invasive species that are aesthetically and horticulturally suitable alternatives to invasive species in your region.


3.    Eliminate specification of species that are invasive in your region.


4.   Be aware of potential environmental impacts beyond the designed and managed area of the landscape plan (e.g. plants may spread to adjacent natural area or cropland).


5.   Encourage nurseries and other suppliers to provide landscape contractors and the public with non-invasive plants.


6.   Collaborate with other local experts and agencies in the development and revision of local landscape ordinances. Promote inclusion of invasive species issues in these ordinances.


Actions for the American Society of Landscape Architects (ASLA) Invasive Plants Species Task Force:


1.   Encourage and work with Landscape Architecture degree programs to uniformly identify and address invasive species in plant materials courses.

a.   Work with Council of Educators in Landscape Architecture to conduct survey of Landscape Architecture programs to determine need for improvements (e.g., ecological concepts, invasiveness, and the use of alternatives). Bill Fountain, University of Kentucky, and the task force will create survey format and ASLA will facilitate communications with CELA president regarding implementation of survey and dissemination of results. 

b.   Work with CELA to include issue of invasiveness in that organization's publications and/or within its annual conferences.


2.   Include invasive species issues in continuing education opportunities for practicing Landscape Architects (e.g. annual meeting, workshops, continuing articles in LA Magazine, and further information sharing derived from interaction with nursery, arboretum, botanic garden, and conservation communities. 


3.   Include on ASLA website: links to sites discussing methods for risk assessment and other IS issues.


4.   Work to include knowledge of invasive species and alternatives in existing certification systems for professionals. (e.g. LARE, International Society of Arboriculture Arborist Certification Program).


Voluntary Codes of Conduct

For Botanic Gardens and Arboreta

February 2002




1.       Conduct an institution-wide review examining all departments and activities that provide opportunities to stem the proliferation of invasive species and inform visitors. For example, review or write a collections policy that addresses this issue; examine such activities as seed sales, plant sales, book store offerings, wreath-making workshops, etc.


2.       Avoid introducing invasive plants by establishing an invasive plant assessment procedure. Predictive risk assessments are desirable, and should also include responsible monitoring on the garden site or through partnerships with other institutions. Institutions should be aware of both direct and indirect effects of plant introduction, such as biological interference in gene flow, disruption of pollinator relationships, etc.


3.       Consider removing invasive species from plant collections. If a decision is made to retain an invasive plant, ensure its control and provide strong interpretation to the public explaining the risk and its function in the garden.


4.       Seek to control harmful invasive species in natural areas managed by the garden and assist others in controlling them on their property, when possible.


5.       Promote non-invasive alternative plants or, when possible, help develop non-invasive alternatives through plant selection or breeding.


6.       If your institution participates in seed or plant distribution, including through Index Seminum, do not distribute known invasive plants except for bona-fide research purposes, and consider the consequences of distribution outside your biogeographic region. Consider a statement of caution attached to species that appear to be potentially invasive but have not been fully evaluated.


7.       Increase public awareness about invasive plants. Inform why they are a problem, including the origin, mechanisms of harm, and need for prevention and control. Work with the local nursery and seed industries to assist the public in environmentally safe gardening and sales. Horticulture education programs, such as those at universities, should also be included in education and outreach efforts. Encourage the public to evaluate what they do in their own practices and gardens.


8.       Participate in developing, implementing, or supporting national, regional, or local early warning systems for immediate reporting and control. Participate also in the creation of regional lists of concern.


9.       Botanical gardens should try to become informed about invasiveness of their species in other biogeographic regions, and this information should be compiled and shared in a manner accessible to all.


10.   Become partners with other organizations in the management of harmful invasive species.


11.   Follow all laws on importation, exportation, quarantine, and distribution of plant materials across political boundaries, including foreign countries. Be sensitive to conventions and treaties that deal with this issue, and encourage affiliated organizations (plant societies, garden clubs, etc.) to do the same.


The Workshop on Linking Ecology and Horticulture


Prevent Plant Invasions”


December 2002



List of Participants



Mr. William Allen

Science Writer

St. Louis Post-Dispatch

St. Louis, Missouri


Ms. Betty Alloway

Federated Garden Clubs of Missouri

St. Louis, Missouri


Mr. Tony Avent

Plant Delights Nursery

Juniper Level Botanic Garden

Raleigh, North Carolina


Ms. Jocelyn Ball

Kansas City Parks and Recreation

Kansas City, Missouri


Mr. Richard Barrett

Blue Hills Landscape Consulting

Overland Park, Kansas


Ms. Yvonne Baskin

Science Writer

Global Invasive Species Programme

Bozeman, Montana


Ms. Rebecca Bech

USDA National Invasive Species Council

Washington, DC


Mr. Pierre Bennerup

Sunny Border Nurseries, Inc

Jefferson, Ohio


Dr. Robert G. Bruenig

Lady Bird Johnson Wildflower Center

Austin, Texas



Mr. Peter Bristol

Chicago Botanic Garden

Glencoe, Illinois


Ms. Rebecca Conner

Federated Garden Clubs of Missouri

St. Louis, Missouri


Ms. Jennifer Dowdell

American Society of Landscape Architects

Washington, DC


Ms. Kate Fay


Boulder, Colorado


Dr. James Folsom

Huntington Botanical Gardens

San Marino, California


Ms. William Fountain IV

University of Kentucky

Lexington, Kentucky


Mr. John Gaskin

Missouri Botanical Garden

St. Louis, Missouri


Ms. Ann Gibbs

Maine Department of Agriculture

Augusta, Maine


Mr. David Gilchrist

Horticultural Trades Association

London, England


Mr. Hugh Gramling

Tampa Bay Wholesale Growers Assn

Seffner, Florida


Dr. Kayri Havens

Chicago Botanic Gardens

Glencoe, Illinois


Dr. Derald Harp

Southeast Missouri State University

Cape Girardeau, Missouri


Mr. C. Dale Hendricks

North Creek Industries

Landenberg, Pennsylvania


Mr. George Hull

Mountain States Wholesale Nursery

Glendale, Arizona


Mr. Andy Jackson

Royal Botanic Gardens, Kew

England, U.K.


Dr. Kathryn Kennedy

Center for Plant Conservation

Missouri Botanical Garden

St. Louis, Missouri


Ms. Carole Kroger

Garden Club of America

St. Louis, Missouri


Mr. Rick Lewandowski

Mt. Cuba Center for the Study of Piedmont Flora

Greenville, Delaware


Mr. Paul Lewis

Nursery and Garden Industry of Australia

Epping, Australia


Ms. Sandy Lloyd

Dept of Agriculture

Bentley, Australia


Dr. Kimberlie McCue

Missouri Botanical Garden

St. Louis, Missouri


Mr. William McNamara

Quarryhill Botanical Garden

Glen Ellen, California


Mr. John McPheeters

Bowood Farms

St. Louis, Missouri


Mr. Wayne Mezitt

Weston Nursery, Inc.

Hopkinton, Massachusetts


Dr. Harold Mooney

Stanford University

Stanford, California


Mr. Darrel Morrison

University of Georgia

Athens, Georgia


Ms. Laurie Neville

Global Invasive Species Programme

Stanford, California


Dr. Margeret Pooler

US National Arborteum

Washington, DC


Dr. John M. Randall

The Nature Conservancy

Davis, California


Mr. Rod Randall

Department of Agriculture

Bentley, Australia


Dr. Patricia Raven

Missouri Botanical Garden

St. Louis, Missouri


Dr. Peter H. Raven

Missouri Botanical Garden

St. Louis, Missouri


Mr. Craig Regelbrugge

American Nursery and Landscape Assn

Washington, DC


Dr. Sarah Reichard

Center for Urban Horticulture

University of Washington

Seattle, Washington



Ms. Barbara Simonson

Federated Garden Clubs of Missouri

St. Louis, Missouri


Mr. Richard Simonson

Litzinger Road Ecology Center

Kirkwood, Missouri


Ms. Jocelyn Sladen

Garden Club of America

Warrenton, Virginia


Ms. Carol Spurrier

US Bureau of Land Management

Washington, DC


Mr. John Swintosky

Jefferson County Parks and Recreation

Louisville, Kentucky


Dr. Susan Timmins

Department of Conservation

Wellington, New Zealand


Dr. Lisa Wagner

Clemson University

Clemson, South Carolina


Dr. Peter White

North Carolina Botanical Garden

University of North Carolina

Chapel Hill, North Carolina


Ms. Lori Williams

National Invasive Species Council

Washington, DC


Dr. Phyllis Windle

Union of Concerned Scientists

Washington, DC


Dr. George Yatskievych

Missouri Botanical Garden

St. Louis, Missouri




[1] Sponsors and/or financial supporters included: The American Association of Botanical Gardens and Arboreta, American Nursery & Landscape Association, American Society of Landscape Architects, Botanic Gardens Conservation International, Center for Plant Conservation, Chicago Botanic Garden, Global Invasive Species Programme, Agricultural Research Service (USDA), Environmental Defense, Missouri Botanical Garden, National Science Foundation, Turner Foundation, Inc, and Winslow Foundation.