Purdue Extension Service

Vanderburgh County, Indiana

Avoid Introducing Invasive Exotic Plants Into Your Garden

By Larry Caplan, Extension Horticulture Educator, Vanderburgh Co, IN

For the Evansville Courier and Press, April 4, 2008

Invasive plants are those that are not native to an area and have negative effects on the environment, human health, or the economy. Mind you, not all non-native plants are harmful. However, some plants grow and reproduce rapidly when introduced to a new area.

If left unchecked, invasive plants will outcompete native plants. This changes the appearance and makeup of our fields and forests, and reduces the food for wildlife. For example, deer avoid the invasive Japanese barberry or Asian bush honeysuckle. To survive, the deer must over-feed on the dwindling supply of native plants, invade our farms and gardens, or starve to death.

Many nature lovers enjoy hiking or biking through parks and woodlands to see the vast array of native wildflowers. Other folks enjoy hunting for morels and other mushrooms and wild herbs. But a single species of invasive plant, such as garlic mustard, can wipe out the diversity and leave us with a boring monoculture.

Hunters have long known that an invasive species, such as Russian olive, will squeeze out oaks and other nut trees. Fewer nut trees means reduced habitat for deer, squirrel, grouse, and turkey. Invasive water grasses, such as reeds and phragmites, greatly reduce the numbers of ducks and geese along our waterways. Eurasian watermilfoil can clog ponds and lakes, decreasing fish populations and interfering with swimming, boating, and other recreational activities.

Some invasives not only squeeze out native plants, but they smother and crush them, too. Kudzu can cover acres of land, killing trees and knocking them down with the weight of the vines. Honeysuckle vines can girdle and kill young trees, and smother native shrubs.

While many folks know about the toxic properties of the native poison ivy, we are getting more complaints about serious burns from giant hogweed, which has invaded the Midwest. Sap from leafy spurge causes eye irritations, and spines from Canada thistles can puncture skin.

Part of the problem with invasive plants is that it's hard to convince people not to move them around. Gardeners see the beauty of purple loosestrife or honeysuckle and plant them in their gardens; highway crews plant crown vetch for erosion control. Hikers pick up seeds of burdock on their clothes; boaters accidently move waterweeds and zebra mussels to new lakes.

Gardeners, foresters, hikers, and other lovers of nature should learn to identify invasive plants, so that they can be destroyed as early as possible. The longer the weeds grow, the more expensive it will be to control them. Check for seeds or plant parts on your clothes, boat, or garden equipment when leaving an infested area, and dispose of these hitchhikers in the trash. And avoid planting invasive exotics in your gardens or woodlots.

The Purdue Extension Service will have a booth at this weekend's 5/3 Home Show. Master Gardeners and I will be on hand to provide information on identifying invasive plants, and coming up with suitable substitutes.