In Ohio, Michigan, Indiana, and Illinois, some plants aren’t as friendly as they seem. In fact, they can quickly take over yards, gardens, and natural spaces if you’re not careful.
Spotting them early can save your garden and local ecosystems a lot of trouble. Let’s take a closer look at the plants you’ll want to keep an eye on this season!
1. Japanese Knotweed
Looking innocent with bamboo-like stems and heart-shaped leaves, this aggressive plant can grow through concrete and asphalt. Found throughout Michigan’s Upper Peninsula and southern Ohio, it spreads rapidly via underground rhizomes.
Just one tiny fragment can create a new colony that’s nearly impossible to remove. Indiana conservation groups spend thousands annually battling this invader, while Illinois homeowners watch property values drop when knotweed appears nearby.
2. Purple Loosestrife
With stunning purple flower spikes that bloom from July through September, this deceptive beauty fools many gardeners. Each plant produces over two million seeds that spread easily across Indiana wetlands and Ohio riverbanks.
Michigan’s Department of Natural Resources considers this one of their most problematic wetland invaders. In Illinois, biological control using specialized beetles has shown promise in managing infestations without harming native plants nearby.
3. Garlic Mustard
Early settlers brought this European herb for cooking and medicine, unaware of its invasive potential. Now it carpets forest floors across Michigan and Indiana, releasing chemicals that prevent native plant growth.
The triangular, toothed leaves emit a garlic smell when crushed. Ohio organizes annual pulling events each spring before the plants flower, while Illinois researchers study how this invader disrupts relationships between native plants and soil fungi.
4. Common Buckthorn
Originally planted as ornamental hedges, these shrubs now dominate woodland edges throughout Illinois and Michigan. The glossy leaves stay green late into fall, allowing buckthorn to photosynthesize longer than native species.
Black berries produced in autumn act as powerful laxatives in birds, spreading seeds widely. Indiana forest managers prioritize removal of female buckthorn trees first, while Ohio woodland owners often find dense thickets blocking access to their property.
5. Multiflora Rose
Don’t be fooled by the delicate white flowers that bloom each June across Indiana hillsides. This thorny shrub forms impenetrable thickets that can reach fifteen feet high, preventing livestock from accessing pasture areas.
Originally promoted for erosion control in Michigan and Ohio, it quickly escaped cultivation. Illinois farmers battle this prickly invader that can produce up to a million seeds per plant, each remaining viable in soil for up to twenty years.
6. Tree of Heaven
Despite its heavenly name, this fast-growing tree creates hellish conditions for native plants. The distinctive smell of its crushed leaves resembles rancid peanut butter or burnt popcorn, helping with identification across Ohio neighborhoods.
Female trees produce thousands of wind-dispersed seeds. Michigan road crews battle root sprouts that emerge after cutting, while Indiana and Illinois officials worry about its role as preferred host for the destructive spotted lanternfly.
7. Reed Canary Grass
Hiding in plain sight along Michigan and Indiana waterways, this tall grass outcompetes native species by forming dense mats of roots and releasing toxins into the soil. The hollow stems and distinctive seed heads can reach over six feet tall.
Ohio wetland restoration projects often begin with controlling this aggressive invader. Illinois conservation groups have found that repeated burning or mowing followed by targeted herbicide application works best for managing large infestations.
8. Autumn Olive
Silver-speckled leaves shimmer in the breeze along Indiana roadsides, making this shrub deceptively attractive. Birds eagerly devour the red berries, spreading seeds across Michigan natural areas and Ohio parks.
Initially planted for wildlife habitat and erosion control, it fixes nitrogen in soil, changing conditions for native plants. Illinois land managers have found that cutting followed by herbicide treatment on stumps works better than trying to pull established plants.
9. Glossy Buckthorn
Wetlands across Michigan and Illinois fall victim to this European shrub with shiny leaves and black berries. Unlike common buckthorn, it thrives in soggy conditions, forming dense stands that shade out native sedges and wildflowers.
The berries contain emodin, a natural laxative that ensures birds spread seeds efficiently. Ohio wetland managers often find seedlings emerging after restoration work, while Indiana conservation groups recommend repeated cutting followed by targeted herbicide application.
10. Callery Pear
Every spring, white blossoms cover these trees along Indiana highways and Ohio suburbs. What started as the ornamental ‘Bradford’ pear has cross-pollinated with other varieties, creating wild offspring that invade natural areas.
The weak branch structure makes them prone to storm damage in Michigan communities. Illinois has recently banned sales of these trees, recognizing how quickly they spread from landscaped areas into fields and forests throughout the Midwest.
11. Phragmites
Towering up to 15 feet tall, these feathery-topped reeds create monocultures in wetlands across Michigan’s shorelines and Indiana marshes. The dense growth blocks sunlight and changes hydrology, eliminating habitat for waterfowl and other wildlife.
Underground rhizomes can extend over 60 feet, making control extremely difficult. Ohio wetland managers use specialized equipment to apply herbicide without damaging surrounding vegetation, while Illinois conservation groups coordinate regional control efforts across watershed boundaries.
12. Japanese Barberry
Red-leafed varieties remain popular in Michigan and Ohio landscapes despite their invasive nature. The small thorns and dense growth make perfect hiding spots for mice, which carry ticks that spread Lyme disease.
Studies in Indiana show areas with barberry have 120 times more disease-carrying ticks than areas without it. Illinois nurseries now promote native alternatives like ninebark and chokeberry that provide similar landscape benefits without ecological damage.
13. Amur Honeysuckle
Early spring leaves make this shrub easy to spot in Indiana and Ohio forests before native plants wake up. The red berries lack nutritional value for migrating birds yet are consumed and spread widely across the Midwest.
Dense shade prevents forest regeneration, creating bare soil prone to erosion. Michigan volunteers organize “honeysuckle pulls” each fall when the shrubs are easiest to identify, while Illinois forest preserves use prescribed fire to control seedlings.
14. Dame’s Rocket
Often mistaken for native phlox, this garden escapee sports four-petaled purple flowers instead of phlox’s five petals. Found throughout Michigan roadways and Illinois woodland edges, it forms dense colonies that crowd out spring wildflowers.
The fragrant blooms attract many pollinators away from native species. Ohio garden clubs now educate members about proper identification, while Indiana parks departments remove these plants from natural areas before they set seed in early summer.
15. Oriental Bittersweet
Bright orange berries make this vine popular in fall decorations, spreading seeds to new locations across Ohio and Michigan. The twining stems can strangle and eventually kill mature trees by girdling trunks and weighing down branches.
Often confused with native American bittersweet, the invasive variety has berries along the stem rather than at branch tips. Indiana forest managers prioritize early detection, while Illinois conservation groups warn against using the vines in holiday wreaths.
16. Canada Thistle
Despite its name, this aggressive thistle originated in Europe, not Canada. The extensive root system can reach 20 feet deep in Michigan soils, making it nearly impossible to remove by pulling or digging.
The fluffy seeds float on wind currents across Indiana farm fields and Illinois natural areas. Ohio agricultural officials consider this one of the most economically damaging weeds, requiring consistent management through mowing before flowering and targeted herbicide application.