Beware of plant invaders

Rob Zimmer Special Contributor
Now Media Group

Across Wisconsin, our wetlands, grasslands and forests are under attack from a variety of alien plant invaders. These are plant and animal species that are not native or indigenous to our area, but were brought here, either purposely or by accident, and allowed to escape and thrive.

June is Invasive Species Awareness Month, a month dedicated to education and eradication projects to help slow the spread of some of the most threatening plant and animal species.

Here is a sampling of the most concerning invasive species locally.

Garlic mustard

One of the most prolific and destructive invasive species found in Wisconsin, garlic mustard has spread and overtaken untold numbers of acres of pristine woodland and forest edge.

The danger with garlic mustard is that it rapidly smothers or suffocates large areas of open woodland, essentially sucking the life out of native wildflowers and grasses on the forest floor.

Beloved wildflowers such as trillium, bloodroot, hepatica, wild ginger, jack in the pulpit and others are wiped out by this suffocating blanket of dense growth.

As is the case with all invasive species, there is no easy method of control. Once this plant has invaded an area and gone to seed, it will take season after season of constant pulling of plants before they go to seed to make an impact.

Dames rocket

Related to garlic mustard, this plant features beautiful, colorful blooms in purple, lavender and white. Sometimes referred to incorrectly as 'wild phlox,' Dame's rocket was extensively planted as erosion control along roadsides prior to its designation as an invasive species.

Hand-pulling of plants before they go to seed is necessary when this plant invades your property.

Japanese knotweed

A large and imposing clump of arching, bamboo-like fronds characterizes Japanese knotweed where it invades forest edges.

These plants may easily reach 8 to 10 feet in height, with large, heart-shaped leaves and masses of airy white blooms along the stems later in the summer.


One of the most well known invaders of our woodlands here in Wisconsin, two species of buckthorn have forever changed our forest landscapes. Glossy buckthorn and common buckthorn, both extensively used as ornamental plants decades ago, quickly escaped into the wild where are they now suffocate massive sections of woodland habitat.

Continuous cutting of saplings and mature trees is needed for multiple years to keep buckthorn under control.

Purple Loosestrife

This wetland Invader remains a tremendous threat to our local marshes, wetlands and river edges. Like its fellow invaders on dry land, purple loosestrife does its damage by smothering out native aquatics.

It is important to pull or remove these plants before they flower and set seed. Each plant may contain well over 100,000 seeds, each so fine that it may be carried by wind and water to new destinations.

Creeping Bellflower

A popular garden plant, creeping bellflower features tall stalks loaded with bell-shaped purple blooms. This plant gets its name by its method of spreading via underground rootlets and shoots that quickly sprout up and cover vast areas.


A large and imposing invasive grass, phragmites is often mistaken for pampas grass. Massive colonies of this extremely tall invasive grass may be seen along area highways and waterways where it thrives.

A new class of invaders

The Wisconsin Department of Natural Resources has released a new listing of invasive plant species. You can view or download this listing, as well as obtain a wealth of information on all regulated invasive species on the DNR website at www.dnr.wi.gov.

Some of the plants recently added to the list of regulated plant species may surprise many gardeners, as they are classic garden and landscape staples.

These include many varieties of trees, shrubs and vining plants, such as Chinese and Japanese wisteria, many cultivars of Japanese barberry, burning bush and others.

Find Rob Zimmer online at www.facebook.com/RobZimmerOutdoors, or at www.robzimmeroutdoors.com.