by Jo Ellen Meyers Sharp

Throughout the Midwest, several plants that were sold as ornamentals for our landscapes have become invasive monsters, which destroy natural habitats and threaten delicate ecosystems.

The U.S. National Arboretum defines invasive plants as those that have "the ability to thrive and spread aggressively outside its natural range. An invasive species that colonizes a new area may gain an ecological edge since the insects, diseases and foraging animals that naturally keep its growth in check are not present in its new habitat."

In the Midwest, one of the worst offenders is purple loosestrife (Lythrum salicaria), a lovely perennial with tall, long-blooming flowers. It has escaped our backyards and taken root in wetlands from Minnesota to Ohio and beyond.

Purple loosestrife produces millions of seeds, which are spread by wind, water and animals. It quickly forms large monocultures and eliminates habitats of native wildlife, including amphibians and certain butterflies.

Purple loosestrife, which came from Europe and Asia, was readily available through seed merchants and garden centers until recently. In the last 20 years, at least 24 states have banned the sale and planting of the perennial, including supposedly sterile cultivars, such as the popular "Morden" series.

Indiana, Michigan, Minnesota, Wisconsin, Iowa and Ohio have either banned the plant altogether, allow planting only with a permit, or declared it a noxious weed.

That means it's illegal to cultivate, divide or share it with friends. Purple loosestrife has no natural predator, but researchers are studying how effective an imported beetle is in controlling the plants. The Nature Conservancy estimates about $45 million a year is spent to control the perennial.

Garlic mustard (Alliaria petiolata) was brought to the United States by Europeans as a food plant. However, this is one scary biennial. The Michigan State University Extension service says many consider it to be one of the most potentially harmful and difficult to control invasive plants in the region.

It starts out as low-growing leaves, called a rosette, in year one. It blooms in year two and spreads its seeds to form huge colonies in woodlands. Garlic mustard smothers native spring ephemerals, such as trilliums, spring beauties and trout lilies.

Several invasive Asian species of honeysuckle shrubs (Lonicera maackii, L. morrowii and L. tatarica) leaf out earlier than native plants and they retain their foliage longer. They shade out native species, keeping them from blooming and propagating naturally. Some emit a poisonous substance that keeps other plants from growing around them.

The Japanese honeysuckle vine (L. japonica), which smells heavenly, creates tangled pathways and strangles native perennials and shrubs in woodlands, parks and other natural areas.

What should you do if you have any of these plants in your landscape? Get rid of them by pulling them out, chopping them off, or in some cases, treat with herbicides. Be prepared — it may take several years to get the invasives under control.

For more information about these plants, visit the Center for Invasive Species and Ecosystem Health, invasive.org.

Sometimes known as the Hoosier Gardener, Jo Ellen Meyers Sharp lives in Indianapolis and is part owner and editor of Indiana Living Green magazine. Her work has also appeared in many other publications, including The American Gardener, Garden Gate and Greenhouse Grower. Meyers Sharp also speaks about gardening and sustainable living throughout the Midwest and is a director of the Garden Writers Association.