Invasive plants are a major threat to the health and diversity of Illinois’ native wildlife. Introduced from faraway lands and lacking natural predators, non-native species have spread into woodlands, prairies, and more, disrupting the balance of our local ecosystems.
In this blog post, we’ll share a few of the most common invasive plants in northeastern Illinois, offer tips for removal, and suggestions for native plants to take their place in your garden.
7 Invasive Plants in Illinois We Need to Remove
Common Buckthorn (Rhamnus cathartica), Glossy Buckthorn (Frangula alnus)
Buckthorn is a large shrub or tall tree with oval leaves with deep veins. As the name suggests, their branches bear thorns. In the late summer, Buckthorn produces black berries that birds eat and spread.
Buckthorn is a common tree in yards as well as local natural spaces. According to the Chicago Region Trees Initiative, “Buckthorn alone accounts for more than one-third of the Chicago region’s trees!” When left unchecked, Buckthorn will form dense thickets and outcompete native plants.
We can control Buckthorn in a few ways. Prescribed fire can help kill seedlings and shrubs, but it must be done regularly to be effective. Another option is to cut down the tree and treat the stump with herbicide. If not treated, Buckthorn will vigorously re-sprout. For an efficient approach, you can target female Buckthorn plants for removal. Only the female plants produce seeds, so by going after them first, we can slow their spread.
Bush Honeysuckles: Tartarian (Lonicera tatarica), Amur (L. maacki), and Morrow (L. morrow); also Vine Honeysuckle: Japanese Honeysuckle (Lonicera japonica)
Origin: Europe and Asia
You can identify a Honeysuckle shrub from its opposite leaf arrangement, light-colored bark, and white to yellow flowers along their branches.
Introduced as an ornamental landscape plant, Honeysuckle has escaped into woodlands and forests, where it can form dense thickets. Honeysuckle (and Buckthorn too) leaf out earlier and keep their leaves later than most other plants. Especially when growing densely, Honeysuckle shades out native plants, like our early spring woodland wildflowers, and takes away resources from trees.
However, there is a species of Bush Honeysuckle native to Illinois, Diervilla lonicera. To be sure you’ve correctly identified it, cut a stem and peer inside. If the stem is hollow, it’s a non-native, invasive Honeysuckle. If the stem is solid, you’ve found the native species.
3. Garlic Mustard
Garlic Mustard is an herbaceous (non-woody) biennial plant, meaning it has a two-year lifespan. Second year plants have a cluster of tiny white flowers with four petals at the top of each plant in April or May. Since each plant can produce thousands of seeds, it is a fast-spreading weed. Garlic Mustard can grow in dense patches, blocking natives, depleting soil nutrients, and even releasing allelopathic compounds that hurt nearby plants.
The easiest way to combat Garlic Mustard is to pull second year plants before they produce seeds. Take care to discard the plants appropriately, such as in a municipal yard waste collection. Garlic Mustard will make seed pods even after it’s pulled!
4. Multiflora Rose
Also called Japanese Rose (Rosa muliflora)
Origin: Eastern Asia
Muliflora Rose is a shrub with climbing, thorny canes. You can find Multiflora Rose forming dense thickets in open woodlands, forest edges, fields, and roadsides—crowding out native plants in the process.
Its clusters of white, five-petaled flowers bloom May to June. It only takes a single plant for Multiflora Rose to start spreading since it can self-pollinate and produce a large quantity of seeds.
Smaller plants can be pulled or dug up. Cutting and mowing will slow their growth, with repeated cuttings being more effective for preventing their reproduction.
5. Autumn Olive
Origin: Eastern Asia
Autumn Olive is a woody shrub that grows up to 20 feet tall. The undersides of their leaves are silvery, making it easy to identify. Its white tubular flowers in late spring to early summer later form red fruits in abundance. Birds eat and disperse the seeds, spreading Autumn Olive throughout fields, thin woodlands, savannas, and roadsides. Autumn Olive can adapt to a range of pH in the soil and higher levels of salt.
Control Autumn Olive by pulling or digging out young saplings. Their entire root system needs to be removed for removal to be effective. You can also cut it and apply herbicide to the stump. Autumn Olive, like many other invasive shrubs, readily re-sprouts if herbicide is not applied to the cut stump.
6. Burning Bush
Origin: Northeastern Asia
Burning Bush is a popular ornamental shrub, known for its bright red fall color, that is still commonly sold and planted today. Its invasive tendencies are a growing issue for Illinois natural spaces. Birds carry seeds to natural areas where Burning Bush can grow under woodland canopies.
Fortunately, Burning Bush seems easier to control than other invasives. Pull out seedlings, dig out most of the root system, or cut stumps and treat with herbicide.
7. Bradford Pear
Also called Callery Pear (Pyrus calleryana), several cultivars
Bradford Pear is a cultivar of Callery Pear that was breed for its showy flowers, rounded tree crown, and lack of thorns. However, it has proven to be a less than ideal landscape tree. It has weak branches that tend to collapse in wind and snow storms, causing it to have a shorter lifespan and require more maintenance. Also, many people aren’t fond of its flowers strong-smelling, rotten fragrance in the spring.
Bradford Pears also have a significant environmental impact. No caterpillars feed on Bradford Pear leaves, so there is a food desert for moth and butterfly caterpillars in parks and road divisions where lines of these trees are planted. The Bradford cultivar was bred to be sterile and not self-pollinate. However, they can pollinate other pears. The resulting hybrids have spread rapidly, crowd out native plants, and produce thorns that can pierce car tires.
The sale of Bradford Pear is now banned in a few states, most recently South Carolina, Ohio, and Pennsylvania. If you have a Bradford Pear, consider cutting down the tree and replacing it with a native flowering tree or shrub.
Banned Plants in Illinois
Some of these plants, like Burning Bush and Bradford Pear, are often sold and planted in Illinois today. On the other hand, some are banned within the state.
Under the Illinois Exotic Weed Act, the following plants cannot be legally bought, sold, distributed, or planted without a permit: Japanese honeysuckle, multiflora rose, purple loosestrife, common buckthorn, glossy buckthorn, saw-toothed buckthorn, dahurian buckthorn, Japanese buckthorn, Chinese buckthorn, kudzu, exotic bush honeysuckles, exotic olives, salt cedar, poison hemlock, giant hogweed, Oriental bittersweet, teasel, and knotweed.
What to Plant Instead
It might be difficult to say goodbye to certain invasive plants with pretty flowers or vibrant fall color. However, the harm invasive plants do to natural spaces makes them a bad choice for your landscaping. Instead, we can choose just as beautiful native plants to take their place in our gardens. Here are a few options for native species to plant instead:
Flowering Native Trees and Shrubs
- Eastern Redbud (Cercis canadensis)
- Native Viburnums (Viburnum spp.), like Nannyberry (V. lentago) or Arrowwood Viburnum (V. dentatum)
- Serviceberry (Amelanchier laevis or A. arborea)
- New Jersey Tea (Ceanothus americanus)
Native Shrubs with Fall Color
- Eastern Wahoo (Euonymus atropurpureus)
- Black Chokeberry (Aronia melanocarpa)
- Spice Bush (Lindera benzoin)
- Allegheny serviceberry (Amelanchier laevis)
Have You Replaced Invasives with Natives? Get Conservation@Home Certified!
Have you removed any of these invasive plants from your yard? If you’ve replaced invasives with native plants, your garden may be eligible for Conservation@Home certification!
Conservation@Home is a program for homeowners who are helping local nature by removing invasives, gardening with native plants, creating wildlife habitat, conserving water, and more. Homeowners who make these earth-friendly choices are certified as a Conservation@Home property and rewarded with a Conservation@Home sign to post in their yard.