5 Invasive Plants that Could be Invading your S.E. Wisconsin Yard

invasive wisconsin plants

Invasive species are detrimental to native ecosystems, by out-competing native species for limited resources. These species can be animals, insects, or plant life. You’ve likely heard about pythons in Florida, wild boars in the south, and carp taking over waterways; meanwhile, the vast majority of invasive plants are more likely to avoid widespread media coverage.

Although invasive plants may avoid media scrutiny, it does not mean they are less of a danger. Invasive plants are categorized as harmful non-native trees, shrubs & herbaceous plants spread through global trade, human/animal transport, and gardening & their entry has negative impacts on the functioning of ecosystems – in ways like: 

  • Putting grazing pressure on native plants, as most non-native plants are not edible for native creatures
  • Threatening local agricultural 
  • Deteriorating soil quality
  • Displacing native species
  • Shading/covering other species below preventing growth 
  • Creating fuel for wild fires

There are a few notable invasive Wisconsin plants in the southeastern region that residents should be on the look out for. 


Five Invasive Wisconsin Plants in Southeastern Region: Description, Methods of Control & Pictures 


invasive wisconsin plants - wild parsnip
Photo by Patrick Lynn

Wild Parsnip

Wild parsnip (Pastinaca sativa) has been documented in Wisconsin since 1900 and is an aggressive member of the carrot family from Europe & Asia. It thrives in areas of high sun and almost any soil type. It’s common in grasslands or near roadsides. The largest issue with this plant, beyond outcompeting native species, is its sap. The sap of the wild parsnip can cause phytophotodermatitis, which is a light reaction; if sap gets on skin that is then exposed to sunlight a rash will appear that can be as mild as reddened skin to as bad as large blisters that may scar. 

What does it look like? 

They’re quite tall around 4 to 5 feet, with large flat clusters of yellow flowers on thick stems 

How does it spread?

Spread of this invasive mostly occurs through seed spread, with actions like mowing down mature plants near roadways also spreading the plant 

How do you control/prevent it? 

Prevention is the best method of control, but it can be removed by pulling or cutting the stem from the roots if the infestation is small – otherwise severing the taproot is also a good way to kill the plant. Removal of the plant may be a multi-year process. 

invasive wisconsin plants - garlic mustard
Photo by Wisconsin DNR

Garlic Mustard

Garlic mustard (Alliaria petiolata) is a plant from Europe that was brought over with the early settlers for culinary (some people do still eat it – here’s a recipe) and supposed medicinal qualitites. It is common in forests, savannahs, yards and roadsides – it likes to grow in places that have some shade, avoiding particularly sunny places. It spreads rapidly as it has a very early season, allowing it to out compete other later growers and very quickly it can overtake the undergrowth. 

What does it look like?

The plant grows 12 to 48 inches tall and its leaves/stem smell like onions or garlic when crushed. The plant is a biennial, meaning it takes 2 years to complete its life cycle. In the first year, it will form a rosette of scalloped, magined leaves that stay semi-evergreen. In the second year, it sends up a flower stem with triangular toothed leaves and tiny four-petaled white flowers. It bears up to 500 seeds per plant, before it dies, that can last up to five years. 

How does it spread?

It is mostly believed to spread through animals, as seeds grab onto their fur before dropping off in a new location. 

How do you control/prevent it?

If you’re encountering a small patch, you can get rid of it through pulling before they flower or cutting the stem if flowering has started. For larger patches, some decide to burn – however as seeds can last up to five years, it is a long process of removal. 


invasive wisconsin plants - reed canary grass
Photo by Wisconsin Wetlands Association

Reed Canary Grass

Reed Canary Grass (Phalaris arundinacea) is considered by experts to be perhaps one of the worst invasives in Wisconsin. It’s a cool season perennial, making its home in wetlands, floodplains, an dry soil in shaded wooded areas. Once in an area, it quickly overtakes any other foliage through sending out runners. Its dense layer of roots can also constrict waterways and limit tree growth.

What does it look like?

Reed canary grass is 2 to 9 feet tall, with a hairless stem & flat leaf blades that taper and 4-8 inches long. The flowers are in dense clusters of florets that change colors from green, to purple, to golden. 

How does it spread?

The grass spreads through seeds dropping or disturbance from waterways, animals, machines or people. However, it also spreads out in the same area through its roots, sending out runners for larger clumps. 

How do you control/prevent it? 

For small patches, it can be pulled, dug or covered for a growing season. For larger areas, mowing can occur three times a season, late spring or late fall burns over 5 to 6 years, or repeatedly tilled for a growing season. There are chemical methods for use as well (although you’ll need to be careful to avoid treating native species). 


purple loosestrife
Photo by iNaturalist

Purple Loosestrife

Purple Loosesrife (Lythrum salicaria) is a fast-spreading European plant, first introduced in the 1800s as a perennial garden plant. Although a pretty, purple flowering species – this plant is a menace to Wisconsin’s habitat. The insects and diseases that impact the plant in its native home are not native to Wisconsin, allowing it to remain unchecked. However, since 1994, the Wisconsin DNR has been using four control species to attempt to regulate this invasive. Two Cella beetles have appeared to be the best insects to use in bio-control for the plant, eating its leaves and shoots. Although it does not eradicate the plant, it has done a good job of managing it and allowing native plants a chance to compete. Residents interested in raising and releasing these bio-control beetles can use the following form to apply.

What does it look like? 

The plant grows to a height of 3 to 7 feet on average, but can get as tall as 12 feet in some cases. It lives for many years, becoming more fiborus with age. The leaves are narrow, arranged on opposite sides of the stem with 50 flowering stems that are magenta pink with 5-7 petals. The blooms begin in July and may last all the way until September. 

How does it spread?

Purple loosestrife produces more than two million tiny seeds per plant, which spread through water or wind. 

How do you control/prevent it?

You can prevent the continued spread by inspecting any items, machines, clothing, etc. that has come in contact with an infected area. To control a small area, a shovel works well to remove the entire plant and root system. Composting is not advised – as it will not kill the plant. There are also some herbicides for use in larger areas. 


 Japanese knotweed
Photo by Kris Olson

Japanese Knotweed 

Japenes Knotweed (Fallopia japonica) is a perennial from Asia that has gone wide and far across the United States. It appeared in Wisconsin in the mid-1900s and has now been noted in most counties. The plant is aggressive and is quickly spreading into more wild areas, threatening riparian areas. It also is noted to threaten foundations and concrete, when grown in an urban environment. 

What does it look like?

These plants are upright and shrub like, growing up to 10 feet tall, with bamboo like stems. The leaves are about 6 inches long and triangular in shape with pointed tip. The flowers are small, greenish-white and arranged in buches with offshoots. 

How does it spread?

The seeds of this plant are spread by wind, water, animals, or humans; however, the plant can also spread through stem fragments or rhizomes. As it has multiple methods of spread, it can be difficult and expensive to combat. 

How do you control/prevent it?

Young plants can be pulled – with speical care to remove any/all rhizomes, as this will produce more plants. This can be difficult with more established plants, as roots can grow down 9 feet and rhizomes out 60 feet from the main plant. It’s possible to eradicate small patches with cutting and pulling, if special attention is taken to ensure all parts of the plant are removed. Larger, more established knotweed will likely require the use of chemical assistance or mass soil removal. 

. . . Is that it?

Unfortunately, there are plenty of other invasive Wisconsin plants in the southeastern area. Therefore, its important that people educate themselves on all the Wisconsin invasive species, to assist in the prevention and control of their spread.

This is a great website resource to learn more about invasive species in Wisconsin and potential control methods. This tool is also a helpful one for identifying any weeds you may encounter that you’re not familiar with.