Conservation Guardians of Northwest Illinois

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Popular Landscape Plants
Threaten Natural Areas
Fall 2009 Newsletter

Millions of Americans enjoy home landscaping and gardening. These activities are a national recreational pastime that pumps billions of dollars into the economy with the purchase of plants, supplies and services. However, an increasing number of popular non-native landscape plants are spreading to natural areas. The invasion by these non-native plants may significantly change the environment of our natural areas.

There are several reasons why landscape plants are becoming a threat to our native landscape. Our increasing human population has caused greater land disturbance and land use. World trade has increased that now allows many more varieties of non-native plants to be imported into the US. Many non-native plants are colorful, fast growing, heat and cold tolerant, long lived (most are perennials), have a high reproductive rate, and they aggressively occupy new areas. These characteristics are ideal for the landscaper that wants to fill an open space quickly.

Landscape plants spread to natural areas by various means. Seeds are carried on the clothing of humans and the fur of animals. Birds eat the fruits and randomly deposit the seeds through defecation. Many plants reproduce by vegetative structure, that is, a small piece of plant will reproduce a new plant. The spread of these invasive plants into natural areas is often evident many decades after introduction. Once established, there are few natural controls of non-native plants in the US.

It may be surprising to learn the species of landscape plants that are invading our natural areas. These include butterfly bush, burning bush, honeysuckle, privet, barberry, wisteria, autumn olive, and Russian olive. There are many others and the list is growing annually. These plants are commercially available in Illinois, but some states have already restricted the sale of some species. Purple loosestrife is a prime example of a non-native landscape plant that has significantly impacted local wetlands. We'll soon be seeing others show up locally as they spread from the urban landscape to adjacent natural areas.

There are associated impacts of introducing non-native plants in the US related to the spread of disease and insect infestation. Japanese beetles were first found in 1912 in New Jersey in a shipment of Japanese iris bulbs and by the late 1980s the beetles had reached the Midwest.

We all know the rest of the story. In 1930, the fungus that causes Dutch elm disease was first found in Ohio in a shipment of logs from France, and by 1970 over 77 million trees had been killed. Our newest threat from Asia, the emerald ash borer, was found in about 1990 in Michigan, has now killed tens of millions of ash trees and is spreading rapidly in the Midwest.

The war on invasive plants in our natural areas is becoming more important than ever due to the increasing number of species and the rapid rate of spread. Currently, over 100 million acres in the US are covered by invasive plants with millions of acres being added each year. Control efforts and follow-up habitat restoration are being impacted by our nation's dwindling dollars for rescue of these natural areas. Volunteers and conservation organizations have become important players in control programs for invasive plants. In addition, state and federal laws now prohibit the sale of some invasive plants.

Home landscapers and gardeners can make a difference in the battle against invasive plants. Learn which landscape plants are invasive to our natural areas and teach others to avoid them. When selecting plants, read the tag and avoid those that are aggressive, self-naturalizing, quick-spreading, non-native (exotic), prolific and pest free. Promote responsible landscaping and gardening by planting native plants that are non-invasive.

—Ed Britton