The basic definition of a weed is a plant growing where it’s not wanted. Certain plants always seem to be categorized as weeds, such as dandelions and garlic mustard, since they really don’t serve a purpose beyond wreaking havoc with our lawns or ornamental plantings. Some undesirable plants have earned the title of being invasive, spreading to the point of causing ill effects to the natural environment.

What is the legal definition for an invasive species? According to the Wisconsin Department of Natural Resources NR 40 law, “A non-native species including hybrids, cultivars, subspecific taxa and genetically modified variants whose introduction causes or is likely to cause economic or environmental harm or harm to human health.” With this in mind, people need to be aware of plants that are considered invasive and should not allow them to grow on their property.

The DNR lists invasive plants as one of the following:

Prohibited: Currently not in Wisconsin, except for a few isolated pioneer stands, but if introduced into our state would probably survive, thrive and spread.

Restricted: Already established in our state and have already or have the potential to harm humans or the environment.

Caution: Not currently regulated and not yet in our state, yet has potential to become invasive.

Non-restricted: Not currently regulated but are already established in the state at the point where control or eradicating is not feasible.

The DNR regulation for prohibited plants deems one “cannot transport, possess, transfer or introduce without a permit.” And for restricted plants, “cannot transport, transfer or introduce without a permit.” Control is required for prohibited species, while only encouraged for restricted plants.

Growing along the roadsides in Kenosha County are populations of many different types of weeds, including some that are considered invasive. A few of these species have pretty flowers, and have enticed unknowing gardeners to transplant them from the “wild” into their home gardens. Once they have become rooted in their new surroundings, they spread and become established to the point of being invasive. By this point, control methods are difficult and even futile.

Dame’s rocket, Hesperis matronalis, also referred to as wild phlox, is often mistaken as a wildflower and is dug out of ditches by gardeners who like the pink, purple or white fragrant blooms. This phlox look-alike is a restricted species that seeds prolifically. It can be differentiated from phlox by the number of flower petals — phlox has five while Hesperis has four.

Other plant inhabitants of our roadsides that are restricted include cut-leaved teasel, crown vetch and purple loosestrife. All were initially introduced for a purpose but escaped cultivation and now have earned the title of invasive. Refrain from transplanting wild plants into your gardens to be sure you aren’t adding more weeds to your landscape.

Jeanne Hilinske-Christensen is the UW-Extension interim horticulture educator for Kenosha and Racine counties. Upcoming events are listed at Submit plant care questions to the Master Gardeners Plant Health Advisers: Phone 262-857-1942 or email