ILLINOIS — Yardwork season is well underway across Illinois and the experts at the Chicago Botanic Garden have a list of unwanted plants for you to exterminate with extreme prejudice.
The expert
When WGN reached out to the Botanic Gardens to ask about the worst invasive plant offenders, they had just the person.
Andrea Kramer is the Director of Restoration Ecology, an Associate Conservation Scientist, and the David Byron Smith Family Curator of Natural Areas at the Chicago Botanic Garden. She holds a Ph. D. in Ecology and Evolution from the University of Illinois Chicago and has been involved with the Chicago Botanic Garden for more than 20 years.
Continue reading to see her answers to our questions.
List of plants with photos
- Buckthorn, both common and glossy (Rhamnus cathartica and Frangula alnus)
- Garlic mustard (Alliaria petiolata)
- Callery or Bradford pear (Pyrus calleryana) – not pictured
- Lesser celandine (Ranunculus ficaria)
- Lonicera spp. (Asian bush/tree honeysuckles)
Common Buckthorn (close-up of berries) – Courtesy: Chicago Botanic Garden 
Garlic Mustard – Courtesy: Chicago Botanic Garden 
Lesser Celandine – Courtesy: Chicago Botanic Garden 
Lonicera spp. – Courtesy: Chicago Botanic Garden 
Buckthorn forest – Courtesy: Chicago Botanic Garden 
Garlic Mustard field – Courtesy: Chicago Botanic Garden 
Lesser Celandine groundcover – Courtesy: Chicago Botanic Garden 
Lonicera spp. full plant – Courtesy: Chicago Botanic Garden
Why they are a threat
The biggest issue with these invasive species is they don’t share well with other plants. This means they can rapidly push out other plants in natural areas where there used to be tens, or even hundreds of plant species. With them also go the thousands of fungi and animal species they in-turn support. This is important to try and prevent because:
- When invasive species replace diverse plant communities, natural areas aren’t as good at doing things like filtering water, storing carbon, and building soil health. As a local example, buckthorn crowds out native plant species in oak woodlands, and without these native species and their deep roots, all that is left is bare ground that easily erodes (see “buckthorn forest” photo).
- Natural areas with diverse plant communities are more resilient to change and stress, such as droughts or flooding, than those with only monocultures of a few invasive species.
- Natural areas where invasive species have displaced native plant communities do not support diverse wildlife, bird, or pollinator communities.
- Plant diversity is also important for human physical and mental health. Sites where invasive species have displaced native plant communities have more mosquitos and ticks. Additionally, our mental health increases when we are around more plant and bird species.
How they get to Illinois
They are so invasive because they are great at spreading beyond where they are planted.
Seeds of Buckthorn, Callery or Bradford Pear, and Lonicera spp. are moved large distances by birds which eat their berries.
A single Garlic Mustard plant produces thousands of tiny seeds that can easily be spread by people or wildlife.
Almost every part of Lesser Celandine can establish a new plant if it is moved to a new place by people or wildlife. As an example, a small root fragment that gets stuck to hiking boots or in a deer hoof can lead to a new population. In order to get rid of this particular species, the entire plant has to be removed both above and below ground, and it needs to be thrown away, not composted or put in landscape waste pickup.
What homeowners can do about invasive plants
First and foremost, make sure you aren’t planting them. If you have any on your property, make a plan to get rid of them and replace with a non-invasive, preferably native species if possible.
Local native nurseries can help identify species that will do well in your yard. To find a local nursery, this tool from Xerces works well.
