Gardeners are becoming more interested in invasive plant issues from two perspectives: To eliminate noxious and other weeds from their gardens, and to avoid planting "ornamental" plants that have the potential to escape from gardens and become invasive. Many gardeners are seeking alternatives to invasive plants.
To combat the sale and spread of invasive plants, Voluntary Codes of Conduct were adopted in 2002. On the individual level, gardeners are becoming aware of the presence of invasive plants in their gardens, and developing a greater interest in native plants and xeriscaping (waterwise gardening, from the Greek "xeros," meaning "dry," plus "-scape").
Many of the qualities that make plants valuable in gardens also make them potential pests. Ease of germination, ease of propagation, hardiness, rapid growth, abundant flowers, and resistance to insects and disease are qualities that are desirable in ornamental plants, yet also are characteristic of weedy plants.
Some of our worst weeds were first introduced as ornamentals; for example, purple loosestrife (Lythrum salicaria), salt cedar (Tamarix spp.), Scotch broom (Cytisus scoparius), tree of heaven (Ailanthus altissima), English ivy (Hedera helix), and pampas grass (Cortaderia selloana). (For several species listed as noxious weeds in Washington see "Meadow in a Can: Does it Really Work?" from the Washington State Noxious Weed Control Board.)
Others show up in wildflower mixes; for example, oxeye daisy (Leucanthemum vulgare = Chrysanthemum leucanthemum), bachelor's button (Centaurea cyanus), yellow toadflax (Linaria vulgaris), and redroot pigweed (Amaranthus retroflexus) (See Wildflower seed mixes contain some wicked bloomers.)
Invasives in the Garden
Be PlantWise is a partnership between the National Park Service, Lady Bird Johnson Wildflower Center, The Garden Club of America, and the National Invasive Species Council to educate the public and communities about best management practices to prevent harmful invasive plants from invading parklands and natural areas. Download PDF of the the PlantWise Brochure (848 KB) or Poster (3.7 MB).
Botanical Bullies: Are weeds hiding in your garden or water garden? Illustrated pdf file from Washington Noxious Weed Control Board.
Bringing Nature Home— How Native Plants Sustain Wildlife in Our Gardens. Douglas W. Tallamy, Timber Press, 11/07, 288p. When native plant species disappear, or are replaced by alien exotics, the insects disappear, impoverishing the food source for birds and other animals. By favoring native plants, gardeners can provide a welcoming environment for wildlife of all kinds.
Cal-HIP: California Horticultural Invasives Prevention. A collaborative effort to address the unwanted spread of horticultural plants into open spaces and wildlands. Friends of the Partnership Newsletter Fall 2005 and Summer 2006.
Control of Invasive Non-Native Plants. Designed for the mid-Atlantic region, but applicable elsewhere; suggests how to evaluate exotic plants for garden use, names many non-native invasive ornamentals, and suggests native alternatives (source: Maryland Native Plant Society).
Cultivating weeds: Is your yard a menace to parks and wildlands? From Science News Online, an article (Nov. 2003) describing how horticultural plants can become invasive.
Eat Those Invasives! Weed recipes from the Mid-Atlantic Exotic Pest Plant Council's Garlic Mustard Cook's Challenge
Garden plants do not become invasive From Horticultural Myths at the Center for Urban Horticulture, University of Washington
Gardening from the National Biological Information Infrastructure (NBII), a comprehensive page covering many topics, including Invasive Plant Species and Weeds.
Goats in the Garden (Word doc) Advice from a master gardener on using goats for weed control. From Master Gardeners of Tuolumne County Newsletter, July 27, 2004.
Home and Garden Information Center from University of Maryland Cooperative Extension. Includes Invasive Species Alerts and useful links.
Image gallery of some of Australia's worst weed infestations highlights severity of the problem in Australia--excellent landscape photos include garden escapees such as Agapanthus, freesia, and forget-me-not.
Invasive Plants in Your Backyard Five problem species from The Nature Consevancy
Invasive Plants—What Every Gardener Needs to Know Info on plant selection and judging potential invasiveness from the Brooklyn Botanic Garden. Includes Ecology for Gardeners, outlining North American vegetation associations, functions of plant communities, and further reading.
Invasive Terrestrial Garden Plants from Saskatchewan Purple Loosestrife and Invasive Species Project. Identification and control; good pictures.
Jumping the Garden Fence (pdf)--Invasive Garden Plants in Australia and their Environmental and Agricultural Impacts, commissioned by WWF-Australia. Escaped garden plants were found to comprise 70 percent of Australia's total weed population; despite laws and publicity, "many serious environmental and agricultural weeds continue to be imported into Australia," and offered for sale.
Lawn Care without Pesticides Available from Cornell University Extension; suggests techniques for minimizing use of pesticides initially as well as for effectively coping with weeds, insects, and diseases.
Linking Ecology & Horticulture to Prevent Plant Invasions from Center for Plant Conservation.
The Organic Weed Management Website Informs organic gardeners about the biology of garden weeds since understanding the biology of weeds is critical to organic weed management.
Plants to Avoid in Your Garden from the USDA Forest Service Celebrating Wildflowers site.
Pocket guide for weed identification in nurseries and landscapes, by S.A. Gower and R.J. Richardson. Michigan State University IPM publication series. 172 pages; 2007; document E2982. See pdf page examples. Order from MSU Extension at http://www.emdc.msue.msu.edu.
Preventing horticultural introductions of invasive plants: potential efficacy of voluntary initiatives. 2007 article in Biological Invasions. Provides specific recommendations for improving participation in voluntary programs in the horticulture trade.
Retailers drop invasive species. Spring 2007 partnership between Meijer stores and TNC to label119 plants as “Recommended Non-Invasive” tag, along with the Conservancy’s logo. The stores will also remove two invasives from their inventories: the Norway maple and Lombardy poplar.
Risk assessment for invasive species produces net bioeconomic benefits. Proc Natl Acad Sci U S A. 2007 Jan 2;104(1):203-7.Epub 2006 Dec 26. Screening ornamental plants to prevent the introduction of invasive species can save billions of dollars in long-term control costs, according to University of Wyoming Economist David Finnoff, co-author of this paper.
Weeder Features. Compares various types of mechanical weeders (hand weeders, weed twisters, etc.) for those who want to avoid herbicides.
Weeds and the nursery industry. A newsletter from Nursery & Garden Industry Australia discussing the invasive plant problem and the role of the nursery industry in dealing with the problem.
What are Noxious Freshwater Weeds? from Washington Dept. of Ecology. Discusses plants introduced as ornamentals (purple loosestrife, giant hogweed), as water garden plants (parrot feather milfoil), and as aquarium plants (Eurasian watermilfoil, Brazilian elodea, fanwort).
Wildflower seed mixes include some wicked bloomers. From the University of Washington Center for Urban Horticulture.
Worst Invasives Used Horticulturally in the U.S. from the Brooklyn Botanic Garden
Yard and Garden Topics from King County (Seattle) Dept. of Natural Resources and Parks.
Alternatives to Invasive Garden Plants
Control of Invasive Non-Native Plants. Designed for the mid-Atlantic region, but applicable elsewhere; suggests how to evaluate exotic plants for garden use, names many non-native invasive ornamentals, and suggests native alternatives (source: Maryland Native Plant Society).
Don't Plant a Pest! Alternatives to Invasive Garden Plants. Educational brochures designed for California gardens, but suggests alternatives to many invasive plants common in the West. The newest brochure outlines non-invasive alternative aquatic plants for water gardening (pdf).
Garden Alternatives to purple loosestrife. Excellent photos of several alternatives to purple loosestrife from CA Dept. of Food & Agriculture.
Garden Wise: Non-Invasive Plants for Your Garden Illustrated booklet created by the Washington Noxious Weed Control Board and the Washington State Nursery and Landscape Association. Dozens of alternatives, grouped by Herbaceous, Ground Cover & Vines, Aquatic & Wetland, Trees & Shrubs.
IvyOUT (Ivy Off Urban Trees). A comprehensive site from the Washington Native Plant Society; includes alternatives, info on ivy removal, and more.
The Ladybird Johnson Wildflower Center website has added a list of native alternatives to invasive garden plants provided by the Brooklyn Botanic Garden from the book Encyclopedia of Native Alternatives to Invasive Plants.
Native Alternatives from Virginia Cooperative Extension. Many of the species will be familiar in other parts of the country.
Native Alternatives to Invasive Plants in the Brooklyn Botanic Garden All-Region Guides. includes Encyclopedia of Native Alternatives to Invasive Plants, Native and Invasive Plant Q&A, Preventing Plant Invasions, and more.
www.PlantRight.org presents alternatives to invasives for California gardeners and promotes the Voluntary Codes of Conduct for the horticultural industry.
Some selected alternatives for five invasive ornamentals. Illustrated pdf file from Washington Noxious Weed Control Board.
Natives in the Garden
Bringing Nature Home, by Douglas W. Tallamy, Timber Press, 11/07, 288 p. There is an unbreakable link between native plant species and native wildlife. When native plant species disappear, or are replaced by alien exotics, the insects disappear, thus impoverishing the food source for birds and other animals. . . gardeners have the power to make a significant contribution toward sustaining biodiversity. By favoring native plants, gardeners can provide a welcoming environment for wildlife of all kinds.
Chesapeake Ecology Center Althugh the Center is located in Maryland, its website has useful articles on conservation landscaping, "rain gardens" as a better way to manage stormwater, and xeriscaping.
Gardening in Western Washington: Native Plants. From WSU Extension. Covers commercial sources, ethics of collecting native plants, propagation from seed and cuttings, dividing and transplanting, and more.
Gardening with Wildflowers, from USDA Forest Service Celebrating Wildflowers site. Covers basic info, landscape for wildlife, native alternatives, genetic consideration, and more.
Grow Native: Don't Plant a Pest Brochure and website from Arizona Native Plant Society, designed to educate newcomers about non-native invasive species threatening the Sonoran Desert and to suggest native alternatives. Spanish version forthcoming.
Grow Native! Plant Identification for Prairie Plantings. From the Missouri Dept. of Conservation. Photos of seeds, seedlngs, juvenile, and mature plants, and distinguishing characteristics.
Guidebook to the Seeds of Native and Non-native Grasses, Forbs, and Shrubs of the Great Basin (Available in pdf format). BLM, Boise, Idaho.
Guidelines for use of native plants in gardening from Native Plant Society of Oregon
How to Go Organic, from the Organic Trade Association. An online collection of existing resources for anyone exploring how to go organic.
Information about Plants from Montana NRCS includes several documents on native plants and landscaping with native plants.
Landscaping with Native Plants of the Intermountain Region Comprehensive 47-page publication from Idaho BLM, available through free download (five pdf files). Also found on Idaho Native Plant Society website.
Let Them Eat Leaves. An NPR article (by Ketzel Levine, NPR correspondent) reviewing the book Bringing Nature Home which mentions the value of backyard native plants for supporting beneficial insects and other wildlife (11/07).
Native Alternatives from Virginia Cooperative Extension. Many of the species will be familiar in other parts of the country.
Native Alternatives to Invasive Plants. Handbook from Brooklyn Botanical Garden. Lists hundreds of native trees, shrubs, vines, herbaceous plants, and grasses, organized by plant type. "Attributes at a Glance" highlights each plant's most attractive features; includes growing advice. $8.95 from BBG.
Native Gardening and Invasive Plants Guide from National Wildlife Federation. Find native plants suitable for your state.
Native Groundcovers and native perennials from the Brooklyn Botanic Garden. Good advice for use in the garden; links to suppliers.
Native Plant Information Network, sponsored by the Lady Bird Johnson Wildflower Center. The goal of NPIN is to assemble and disseminate information that will encourage the cultivation, conservation, and preservation of wildflowers and other native flora throughout North America.
Native Plant Nurseries in Washington State compiled by the Water and Land Resources Division of King County, WA
Native Plant Resources for the Pacific Northwest provided by the Water and Land Resources Division of King County, WA.
Native Plant Salvage Program King County (Seattle) WA. Volunteers rescue plants from construction sites and later replant at locations around the County. Scroll down page for links to "Shrink your lawn with native plants" and more naturescaping info.
Native Plant Crossroads from the Canadian Musueum of Nature has a useful glossary and much more.
Nebraska Statewide Arboretum. A gateway to great gardens. Includes Nebraska FloraSearch, a comprehensive database of Nebraska flowers and grasses. Supports successful gardening and landscaping efforts in Nebraska.
Sources of Native Plants and Seeds on CIPM's Restoration and Revegetation
Urban Forests under Siege. Series of articles on invasive plants in the Seattle Post-Intelligencer. See also To free urban forests from invaders, some weigh ban on noxious plants.
U.S. Regional Guide to organic and sustainable resources. Links to a wealth of resources, from the Organic Trade Association.
"Using local seeds in prairie restoration." Gustafson, D.J., D.J Gibson, and D.L. Nickrent. Native Plants Journal, Spring 2005: 25-28.
Wild Ones Native Plants, Natural Landscapes: promotes the establishment of native communities around homes and businesses, using ecologically sound practices.
Yard and Garden Topics from King County (Seattle) Dept. of Natural Resources and Parks.
Xeriscaping: Low-Water Gardening
Colorado WaterWise Council Xeriscape Colorado is a program of the Colorado WaterWise Council. Xeriscape promotes creative approaches to water conserving landscapes by helping people improve their landscapes and to reduce the need for water, maintenance and other resources. Defines xeriscaping, covers plan and design, low-water plants, and much more. Good links to resources and references.
Guide to Water Wise Gardening from the American Nursery and Landscape Association
Landscape Water Conservation: Xeriscape. From Texas A&M. Includes basic principles, and plant lists for Texas.
Water-Smart Gardening from Denver Botanic Gardens Plant selection; links to CSU Extension
Waterwise Plants for Utah Landscapes From Utah.gov. Lists many native plants and sources. Waterwise Plant List from USU Extension.
Xeriscape Council of New Mexico. The Council's primary goal is to offer education and training about water conservation, primarily through efficient irrigation of xeriscaping utilizing native and other low-water plants.
Xeriscape Gardening. An extensive list of resources from Colorado State Extension Service. Includes plant lists, photos, plants for specific sites, and much more.
Xeriscape Misconceptions Corrected from BASIN (Boulder Area Sustainability Information Network), Colorado.
Xeriscape Plant Selections and Ideas from University of North Dakota Cooperative Extension.
Xeriscaping from California Integrated Waste Management Board. Concentrates on water and other resources that can be saved by xeriscaping. Covers landscape design, irrigation, soil preparation, and more.
Voluntary Codes of Conduct
(Excerpted from Center for Plant Conservation website) In 2001 and 2002, voluntary Codes of Conduct were proposed for government, nursery professionals, the gardening public, landscape architects, and botanic gardens and arboreta at a workshop designed to find ways to reduce the introduction and spread of non-native invasive plants. The entire workshop proceedings and codes of conduct can be found online, or summarized below. Certain findings and principles, known as the St. Louis Declaration, were agreed upon by the entire St. Louis assemblage.
The St. Louis Declaration On Invasive Plant Species
Findings
- 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 (The St. Louis Six)
- Plant introduction should be pursued in a manner that both acknowledges and minimizes unintended harm.
- 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.
- Prevention and early detection are the most cost effective techniques that can be used against invasive plants.
- 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.
- 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.
- 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.
