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Common Buckthorn (Rhamnus cathartica) and Glossy Buckthorn (Rhamnus frangula)
by Dale Crook
COMMON OR EUROPEAN BUCKTHORN (Rhamnus cathartica) and Glossy Buckthorn (Rhamnus frangula), which are classified as highly invasive, are taking over many of the natural areas in Ottawa. Buckthorns form dense thickets, crowding out native shrubs, wildflowers and herbs, often completely obliterating them.
This threat to our natural areas has been ignored for too long. Buckthorn is now widespread in the Greenbelt, along the banks of both the Ottawa and Rideau rivers, along our country roadways, around golf courses, in pastures, in our back yards, and throughout most woodlots. Unless something is done urgently to control this invasive spread, the diversity of our natural areas will be forever changed to the great detriment of our native flora and fauna. This should be of great concern to all naturalists!
At the FWG over the last couple of years, we've made an effort to control and in the long term eradicate buckthorn.
First, learn to recognize the enemy
Both buckthorns are deciduous and grow to about 20 feet in height. Common Buckthorn (top photo) is more profuse and grows in diverse habitats. Glossy Buckthorn (lower photo) typically grows in wetter, less shaded sites.
The buckthorns are extremely invasive. Their tough constitution and rapid growth rate allow it to produce copious amounts of black fruit on relatively young shrubs. They readily reseed producing a multitude of seedlings in densities of 15 to 20 per square foot. The fruit is often consumed by birds (lately deer) and subsequently dispersed to surrounding areas. The leaves stay green and persist late into the autumn. The heartwood is bright orange, the roots are black and shallow.
The buckthorn trees are readily identified, but some care is needed as they resemble wild plums and some cherry trees.
| Common | Glossy |
|---|
| Leaves mostly opposite, 3–5 upcurved veins per side, dark green, minutely blunt-toothed, tips abruptly pointed, slightly folded and curled back | Leaves alternate, 5–10 parallel veins per side, glossy green, smooth edged, slightly wavy. underside of leaves hairy |
| Generally unisexual shrubs, 4-part sepal & flower | Bisexual trees, 5-part sepal & flower |
| Branches rigid with gray-black bark bark, twigs hairless | Branches brittle with brown-green bark, twigs hairy |
| Most branches tipped with a sharp thorn | Branches not tipped with thorns |
| Bark browish-grey | Bark greyish |
Then, remove it
At the FWG, we started working on buckthorn removal in 2000. At that time, it had taken over as the understorey in the Ash Woodlot and in the thickets around the Old Field. Simply cutting it was a waste of time as it resprouted vigorously around the root ball.
The most effective way to remove buckthorn is to uproot it. The Landowner Resource Centre was experimenting with a "weed wrench" that could pull trees up to 2" in diameter, and they kindly allowed us to borrow the device. As buckthorn has shallow roots, saplings could be hand pulled.
Larger trees that were too big for the weed wrench were cut and the stump treated with a Roundup solution. Although the FWG has a policy of not using herbicides, we decided to test this method, which was recommended to us. "Girdling" the trunks (i.e., cutting away the living layer of the bark all the way around) was also tried, but often the tree was not killed and resprouting occurred.
In 2001, a City of Ottawa grant allowed us to buy 3 weed wrenches — mini, light, and heavy. The heavy wrench is often needed, but because of its weight (24 lbs) it is difficult to carry around. The light and mini wrenches are more portable and good for pulling out smaller trees, although these can often be pulled out by hand. The medium wrench has been the workhorse tool.
 Weed wrenches work well where there is no sod, but are less effective in grassy areas. However, we discovered a technique that helps considerably. Using an 8" camp saw pushed down into the dirt, roots are cut all around the tree at about a 12" radius. Trees up to 2.5" in diameter can now be pulled with the weed wrench, thus eliminating the use of the herbicide. Roots left in the ground do not resprout.
The fight to control buckthorn at the FWG will be an ongoing battle for many years. Upfront "soldiers" include Malcolm Leith, Tony and Gretchen Denton, Sandy Garland, Neville Woodman, Jay Ladell, and our summer students, Kim Loenhart and Bruce Craig. Thanks to Malcolm Leith for most of the photographs.
We have built up quite a bit of experience controlling the buckthorn at the FWG which we are willing to share with anyone wanting to undertake buckthorn control. The weed wrenches can also be viewed and tried out. For further discussion, contact us. The website for the weed wrenches is: The Weed Wrench Company. Recently, we found a Canadian company that makes and distributes weed wrenches (see The Extractigator).
Student employee, Bruce Craig, uses weed wrench
to remove young buckthorn trees from our woodlot
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