Invasive species are plants of deceptive beauty

Rob Zimmer

In Wisconsin, June is Invasive Species Awareness Month. The Wisconsin Department of Natural Resources uses the month of June to educate gardeners and property owners on the threat and danger that invasive species pose to native Wisconsin landscapes and ecosystems.

By definition, an invasive species is one that arrived after the first white settlers came to Wisconsin. Many of these plants were brought here for their value as ornamental plants, or as food crops. Others stowed away on ships in the form of seeds, or mixed in with hay and packing material.

While invasive species can include birds, mammals, insects and more, it is invasive plants that get the most attention here in Wisconsin. For gardeners, this is important because many of the plants growing right in our own backyards are technically classified as invasive and should be controlled or eradicated when possible.

Property owners adjacent to woodlands need to be especially watchful of invasive species on their property as, once these plants escape cultivation into our forests, they are capable of a great deal of damage and destruction. Most notably, the biggest threat most invasive species pose is simply smothering out and overcrowding our native wildflowers and plants.

Because invasive species have no natural predators here, they quickly spread and colonize large areas, choking out the understory and smothering native woodland wildflowers such as many of our favorites, trilliums, hepaticas, bloodroot, trout lilies, mayapples, Virginia bluebells and others.

Where invasive species take hold, it is important to realize and understand that there is no quick, one-shot method of eradicating the species, or any poison or product that is going to eliminate them. As long as they took to take hold, they will take at least that long to gain control over.

It is also important to remember that most invasive species are quite beautiful and showy. This is, after all, one of the main reasons they were brought here. Many of our endangered species are beautiful wildflowers and wonderful ornamental trees when they are kept under control. However, once their seeds begin to spread, they become nearly impossible to eradicate.

Garlic mustard and buckthorn are among the most dangerous of all invasive species here in Wisconsin and the most difficult to control.

Garlic mustard is an herbaceous herb that can carpet entire sections of the forest floor within just a few years. It is important not to let these plants go to seed when they are discovered. Each plant can produce untold numbers of seeds that quickly spread and colonize the forest floor. If you have garlic mustard growing in your garden or nearby woodlot, pull as often as possible and prevent back from going to seed by sheering before the plant flowers. Garlic mustard is also delicious and there are many wonderful recipes that you can find online to enjoy this tasty plant.

Buckthorn is even more tricky to control. Because this is a woody shrub, forming massive tangles of intertwined branches, buckthorn is one of the most challenging of all invasive species to control. In addition, songbirds consume the berries, spreading them quickly and prolifically with their droppings.

The best way to treat buckthorn is frequent cutting and treatment with a brush killer such as Tordon. Follow the label directions. This will require several seasons of work and the patience of the gardener or property owner.

Other examples of invasive species here in our area are the bright and colorful Dame’s rocket, a member of the mustard family, as well as phragmites, often called pampas grass, Japanese knotweed, Russian olive, autumn olive, the many introduced bush honeysuckles, canary reed grass, purple loosestrife and others.

The Wisconsin DNR has a wonderful resource online for property owners and gardeners interested in learning more about invasive species. Simply search “Wisconsin DNR invasive species” and you will be taken to a page loaded with information including list of all the technically restricted plants, as well as fact sheets on each one with the recommended control measures and an abundance of photographs to help you identify invasive plants on your property.