As our gardens begin to come into their full beauty, let’s think for a minute about one of their hidden costs: invasive plants.
These are fast-spreading species, usually imported for use in gardens, that do serious harm to our local ecosystems because they reproduce so easily that they take over natural areas and outcompete native plants. “They may start out in gardens, but they don’t stay there,” said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle.
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Invasive plants are a major threat to forest preserves, national parks and other natural areas such as the East Woods and the Schulenberg Prairie at the Arboretum, where they hog sunlight, water and nutrients. “Our staff and volunteers spend a lot of their time removing invasive plants, just so the native plants and the wildlife that depends on them have a chance,” said Spencer Campbell, senior manager of natural areas at the Arboretum. “It’s a never-ending battle.”
May is Invasive Species Awareness Month in Illinois. It’s a good time for gardeners to focus on their role in keeping invasive plants at bay.
Most invasive plants are not the ones we think of as annoying weeds, such as dandelions. Familiar and even beloved garden plants can be seriously invasive, such as Callery or Bradford pear (Pyrus calleryana), burning bush (Euonymus alatus) and reed canary grass (Phalaris arundinacea).
Although most invasive plants are non-native, not all non-native garden plants become invasive. Hostas, from western Asia, and daffodils, from southern Europe, do no harm.
The plants that do pose a problem are those with an especially strong tendency to spread. Often they have huge numbers of tiny seeds or berries that birds like to eat and carry far away. Many invasive plants have another competitive advantage because they leaf out earlier than native plants and their shade can keep native plants’ seeds from sprouting or thriving.
The imported invasive plants are able to spread with impunity because natural forces such as insects, animals and diseases that kept them in check in their native ecosystems were left behind in Europe or Asia.
What can gardeners do to avoid contributing to the problem?
Know the troublemakers: Consult the list of the Midwest Invasive Plant Network (mipn.org), or check plants you’re considering for your garden against the Arboretum’s plant pages at mortonarb.org/search-plants.
Consider removing invasive plants: If you learn that you have any of these problem plants, think about replacing them with plants that don’t pose a threat. Browse for attractive alternatives on the website of the Woody Invasives of the Great Lakes Collaborative (woodyinvasives.org).
Be wary of free plants: A surplus plant passed along by a fellow gardener may be an aggressively spreading invasive species such as reed canary grass or ribbon grass (Phalaris arundinacea var. picta). Before you plant anything, check it out carefully to make sure it is not invasive.
Look for seedless varieties: Plant breeders know that gardeners are increasingly aware of the invasive plant problem, so they are developing more cultivated varieties that are less likely to spread. If you have your heart set on an invasive species, such as barberry, look for a cultivated variety labeled as sterile, so it produces no berries or seeds.
Stay aware: Climate change is intensifying the problem because it means more plants may become invasive. As the climate warms, the growing season gets longer and winters aren’t as harsh, so some species that would once have been killed by freezing may survive here to invade natural areas.
“We have to be constantly alert to new invasive plant threats,” Campbell said. “It’s a moving target.”
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or [email protected]). Beth Botts is a staff writer at the Arboretum.