Exotic, invasive plants may have originally been planted as garden ornamentals or for livestock fodder, but they have since escaped from cultivation and taken over the landscape. Exotic plants crowd out native plant species and often offer little wildlife value. The conscientious gardener will make every effort to remove them from her yard, garden or property. These are just a few of the wild, exotic plants found in Wisconsin.
Common Buckthorn (Rhamnus cathartica)
Originally planted as a landscaping shrub, buckthorn has since moved into the woodlands and fields of Wisconsin. Buckthorn has glossy, oval leaves and dark red or black berries that form close to the stem. Buckthorn may grow as tall as 25 feet, but is more commonly found as a sort, thickety bush. To control buckthorn, pull it out or cut the trunk and paint the stump with herbicide. Burn the brush to prevent it from resprouting.
Garlic Mustard (Allaria petiolata)
Garlic mustard may be found in lawns, but is more likely to invade shady woods and waste areas. This form is usually 12 to 24 inches tall, although it may reach as high as four feet. Garlic mustard can be identified by a cluster of small white flowers and deeply notched leaves that release a garlicky or oniony odor when crushed. Garlic mustard has a long taproot, so wait until the ground it wet to pull it up, as broken pieces of root may regrow. Do not compost garlic mustard. Put it in a tightly sealed plastic bag and throw it away with your garbage. Garlic mustard is also edible and was brought to Wisconsin as a food plant.
Spotted Knapweed (Centaurea biersteinii)
Spotted knapweed is an allelopathic plant, which means that it poisons the soil so that no other plants can grow there. It quickly takes over prairies, meadows, grasslands and roadsides. Look for thin, short leaves and spiky magenta flowers that somewhat resemble thistle flowers on a plant that is about three feet high. Pull up spotted knapweed and dispose of it in plastic bags.
Purple Loosestrife (Lythrum salicaria)
These three to six foot tall purple flowers were grown in flower gardens in the 19th century, but now purple loosestrife poses a serious to Wisconsin's lakes, rivers, streams and other wetlands where it degrades the habitat for fish, birds and other wildlife. Pull or dig up purple loosestrife or, for very large infestations, talk to the Wisconsin Department of Natural Resources (WDNR) about releasing galeucella beetles, which eat purple loosestrife.