If you own property in Northeast Illinois, there's a good chance you've walked past buckthorn without knowing it. Common buckthorn (Rhamnus cathartica) is everywhere: in woodlots, along fence lines, in the understory of suburban forests, and at the edges of nature preserves. It's so pervasive that many people assume it's a native plant. It isn't.
What Is Buckthorn?
Common buckthorn is a deciduous shrub or small tree native to Europe and western Asia. It was introduced to North America in the 1800s as a popular ornamental hedging plant. By the mid-20th century, ecologists began recognizing what a problem it had become.
There are two species you'll most commonly encounter in Illinois:
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Common buckthorn (Rhamnus cathartica): the more widespread of the two. Grows up to 20-25 feet tall. Has distinctive thorns at the tip of its branches (which is how it got its name). Leaves are oval with slightly toothed margins and stay green well into fall.
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Glossy buckthorn (Frangula alnus): typically found in wetter areas, like floodplains and wetland edges. Lacks thorns. Has shiny, dark green leaves with smooth margins.
Both species produce abundant dark berries that birds eat and spread widely, making them extremely difficult to contain once established.
Why Is It So Harmful?
Buckthorn's competitive advantage comes from several traits that allow it to out-compete native plants:
Early leaf-out and late leaf-drop. Buckthorn leafs out earlier in spring and holds its leaves later into fall than most native plants. This extended growing season gives it more time to photosynthesize and shade out competitors.
Dense shade. A mature buckthorn thicket creates such heavy shade that very few native understory plants can survive beneath it. This eliminates the diverse layers of shrubs, wildflowers, and tree seedlings that healthy forests depend on.
Allelopathic chemicals. Buckthorn releases compounds into the soil, particularly emodin, that inhibit the germination and growth of competing plant species. This is sometimes called allelopathy, and it gives buckthorn a chemical edge on top of its physical dominance.
Prolific seed production. A single mature buckthorn can produce thousands of seeds per year. Birds love the berries and spread them far and wide. Seeds can remain viable in the soil for years, meaning removal without follow-up treatment often results in dense seedling populations.
No natural enemies. Unlike in its native range in Europe, buckthorn has very few insects or pathogens in North America that significantly limit its growth.
What Does a Buckthorn Infestation Look Like?
In early stages, you might notice buckthorn as a few small shrubs along a treeline or fence. Left untreated, it expands aggressively. In mature infestations, you'll find:
- Dense, nearly impassable thickets with little plant diversity beneath them
- A dark, uniform green understory that crowds out native wildflowers and tree seedlings
- Bare, compacted soil beneath the canopy with little ground cover
- Abundant small thorny saplings emerging from the soil wherever light reaches
By late fall, after native trees have lost their leaves, buckthorn is often clearly visible: still green while everything around it has gone dormant.
What Should You Do?
The good news is that buckthorn can be effectively controlled. The bad news is that control requires a thoughtful, multi-step approach. Removal alone is not enough.
At Beyond Buckthorn, we start every project with an honest assessment of the extent of the problem and a clear plan for both removal and follow-up treatment. Early intervention makes a significant difference: the longer buckthorn goes unmanaged, the larger the seed bank in your soil and the more aggressive the regrowth after cutting.
If you're unsure whether you have buckthorn on your property, or how serious the infestation is, reach out to us. We're happy to walk your land and give you a straightforward assessment at no charge.