All About Invasive Plants

Invasive plants can cause major damage to the ecosystems where we live—yet, not every non-native is bad. Learn how to become an effective protector of your region’s natural biodiversity.


| July/August 2016



canadian thistle

Canadian Thistle is an invasive species which takes over savannas, glades and prairies.

Photo by Wikimedia commons

Most people who garden have heard of invasive plants, but many of us aren’t sure how to identify and eliminate them, or how invasives differ from basic weeds. It’s possible that you’ve even seen the effects of invasives. Maybe you’re in Michigan and have noticed purple loosestrife choking out wetland plants and animals along the shores of rivers and lakes. Or perhaps English ivy has overtaken your flower garden in Oregon. If you live in the South, you’ve no doubt seen acres of land swallowed up by kudzu.

Invasive plants are more than just weeds—weeds are simply plants that interfere with a gardener’s management plan for a particular site (think clover that has sneaked from your yard into your flower bed). Invasive species, according to the USDA, are non-native plants, animals and other organisms spread mostly by human actions and whose introduction is harmful in some way. These aggressive invaders can affect the ecological balance of entire ecosystems as they outcompete native species for food and other resources, spread non-native diseases, eat native species, or kill the young of native species. As a result, they can not only wipe out native flora and fauna, but in some cases also eliminate biodiversity in the landscape.

According to the U.S. Geological Survey, more than 6,500 foreign species of flora and fauna have made themselves at home in the United States in the last century, and some of them are aggressive enough to be considered invasive. One prime example is kudzu. An Asian native, it was planted as an erosion controller in the 1870s (the U.S. Soil Conservation Service promoted its use for erosion control from the 1930s through 1950s). Since then, it has taken over thousands of acres in the East, South and lower Midwest. Kudzu thrives in temperate climates, where it grows at an alarming rate of 50 to 60 feet per growing season, and can climb 100 feet. Its dense coverage enables it to choke out light, water and nutrients from other species, and its height enables it to cover trees as well as low-growing plants. 

How Do Invasives Get Here?

Invasive species take many routes into American ecosystems. Leigh Greenwood, outreach program director with The Nature Conservancy, says they travel as contaminants in seed, grain or hay carried from state to state or country to country. They’ve also migrated in the ballast of ships, and some have been intentionally introduced as ornamental plants or to serve practical purposes, such as providing windbreaks or erosion control. 

Gardeners can unintentionally contribute to the spread of invasives, says Lili Singer, director of special projects and adult education with the Theodore Payne Foundation for Wildflowers and Native Plants in Sun Valley, California. Nurseries sometimes sell plants that qualify as invasive species, and gardeners buy them without realizing the potential negative impact. The English ivy adopted by American gardeners is a good example. It may look lovely growing up the side of a house, but it can also choke out native plants and overtake ornamental gardens.

What Can I Do?

It’s easy for us all to help stop the spread of invasives. First, avoid planting them in your garden. Let’s go back to the English ivy example: If you’re looking for a ground cover, you might read that it’s an excellent choice. But knowing it’s invasive, you might instead use the North American native creeping phlox or choose from a variety of native ferns. You can find a list of plants to avoid and better replacements from the Natural Arboretum: usna.usda.gov/Gardens/faqs/InvasivesAlternatives.html. 





elderberry, echinacea, bee hive

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