Where did buckthorn come from?
Buckthorn is native to Europe and was first brought to Minnesota in the mid-1800's as a hedging material.
It invasive properties were discovered in the 1930's, and buckthorn has not been sold in nurseries since.
There are two main species: Common Buckthorn and Glossy Buckthorn.
Common Buckthorn, also known as European Buckthorn, is the most problematic species. It readily invades woodland understories and the edges of fields or prairies. It can thrive through drought and even in low-sunlight areas.
Both Common Buckthorn and the other main specie, Glossy Buckthorn, are spread easily and rapidly by birds that feed on its fruit and carry the seeds for miles before excreting them in far-away locations where the seeds can grow into new buckthorn infestations.
How can I identify buckthorn?
Common Buckthorn characteristics: Look for egg-shaped, hairless, elliptical leaves that are pointed at the tip, smooth, dark, glossy, and fine-toothed edges.
Common buckthorn is a dioecious species-meaning it has male and female flowers on separate plants. Flowers are typically 4-petaled, yellow-green in color, and are found in 2-8 small inconspicuous clusters. The flowers are born on the short stalks where the leaf meets the twig and are most noticeable in May and June.
The leaves have 3-5 pairs of veins curving toward the tip from the mid-vein. Common Buckthorn remains green well into late fall (even after all the other surrounding trees have lost their leaves). Common Buckthorn often retains its green leaves well into November and sometimes even December in Minnesota. It's also one of the first trees to leaf-out in the spring.
Buds & Leaves are mostly opposite. The twigs of Common Buckthorn often end in sharp terminal spurs, spines, or thorns.
The female trees have large dense clusters of black 1/4 - 3/8 -inch fruit. These ripen in August and September, but can remain on the branches until March.
Common Buckthorn can reach a maximum height of 20-25 feet with a spreading irregular crown.
It has gray/brown, flakey/rough bark with elongated, silvery, cork-like projections (a word of caution: native plums or cherries have a similar bark).
A cut Buckthorn branch exposes yellow sapwood and orange heartwood. This is a telltale sign of Buckthorn. Expose this very distinctive yellow-colored sapwood by scraping a branch any time of the year.
Common buckthorn can grow in uplands, mainly in the understory of oak woods, savannas, riparian woods, and in grasslands. It is often found in disturbed areas such as thickets, hedgerows, pastures, abandoned fields, roadsides and on rocky sites.
Both Common and Glossy Buckthorn tend to fare best in direct sunlight. Though both species easily grow in shady areas, they do grow less densely in areas with less sunlight.
Common Buckthorn grows in the following areas of the United States:
Common Buckthorn grows in nearly every corner of Minnesota:
Glossy Buckthorn characteristics: Look for egg-shaped leaves that are smooth, dark, glossy, and with toothless edges. Their leaves also sometimes have fine hairs on the underside.
The leaves have 8-9 pairs of veins that run parallel from the midrib. Glossy Buckthorn remains green well into late fall (even after all the other surrounding trees have lost their leaves). Glossy Buckthorn often retains its leaves well into November and sometimes even December in Minnesota. It's also one of the first trees to leaf-out in the spring.
Flowers are 5-petaled and greenish-white in color. Flowering takes place from late May until the first frost.
The female trees have large, dense clusters of red 1/4 - 3/8 -inch fruit, which ripen into a blackish, dark purple around August-September, but can remain on the branches until March. Each fruit/berry contains 2-3 seeds.
Glossy Buckthorn can reach a maximum height of 20-25 feet with a spreading irregular crown. Glossy Buckthorn has brown, smooth bark with elongated, silvery, corky projections.
A cut Buckthorn branch reveals yellow sapwood and orange heartwood. As with Common Buckthorn, the sapwood and heartwood immediately tell you you're looking at Buckthorn. Expose this very distinctive yellow-colored sapwood by scraping a branch any time of the year.
Buds/Leaves are mostly alternate and the twigs of Glossy Buckthorn have no spurs or thorns; instead the twigs have buds on their tips.
Although Glossy Buckthorn can withstand drought, it tends to invade wetlands and moist woodlands but also grows well in a wide variety of upland habitats, including old fields, roadsides and dry woodlands. It has become a problem in wetlands as varied as acidic bogs, calcareous fens and sedge meadows. It is capable of growing in both full sun and shaded habitats.
Glossy Buckthorn afflicts about half the states in the US:
It also inhabits most of the counties in Minnesota:
What other names does buckthorn go by?
The Latin name of Common Buckthorn is Rhamnus cathartica. This is the most common specie of Buckthorn found in Minnesota (hence its nickname "Common Buckthorn").
Other less frequently used terms for Common Buckthorn include Highwaythorn, Waythorn, Hartsthorn, and Ramsthorn.
The Latin name of Glossy Buckthorn is Rhamnus frangula. It's not as common in Minnesota because it's typically only found in low-lying areas that hold excess moisture (i.e., wetlands), although it can also be found in drier, upland areas.
Other less frequently used terms for Glossy Buckthorn include: Frangula alnus, Alder Buckthorn, Fen Buckthorn, Black Dogwood, and Frangula Bark.
In what ways is buckthorn harmful?
Buckthorn should be on America's "Most Wanted" list, with its picture hanging up in every US Post Office! Here are a few of the dangers of Buckthorn:
a) Buckthorn squeezes out native plants for nutrients, sunlight, and moisture. It literally chokes out surrounding healthy trees and makes it impossible for any new growth to take root under its cancerous canopy of dense vegetation.
b) Buckthorn degrades wildlife habitats and alters the natural food chain in and growth of an otherwise healthy forest. It disrupts the whole natural balance of the ecosystem.
c) Buckthorn can host pests like Crown Rust Fungus and Soybean Aphids. Crown Rust can devastate oat crops and a wide variety of other grasses. Soybean Aphids can have a devastating effect on the yield of soybean crops. Without buckthorn as host, these pests couldn't survive to blight crops.
d) Buckthorn contributes to erosion by overshadowing plants that grow on the forest floor, causing them to die and causing the soil to lose the integrity and structure created by such plants.
e) Buckthorn lacks "natural controls" like insects or diseases that would curb its growth. A Buckthorn-infested forest is too dense to walk through, and the thorns of Common Buckthorn will leave you bloodied.
f) Buckthorn attracts many species of birds (especially robins and cedar waxwings) that eat the berries and spread the seeds through excrement. Not only are the birds attracted to the plentiful berries, but because the buckthorn berries have a diuretic and cathartic effect, the birds pass the seeds very quickly to the surrounding areas of the forest. This makes Buckthorn spread even more widely and rapidly, making it harder for us to control and contain.
How difficult is it to remove is buckthorn?
Very difficult, for several reasons:
Any efforts to remove buckthorn just by cutting it down are usually unsuccessful. For one thing, buckthorn has an extensive fibrous root system, which allows it to survive dormant in the soil for long periods of time.
Also, if you cut down the buckthorn but choose not to treat the stumps with poison, they will re-sprout vigorously. Within 3-4 years a stump sprout will grow large enough to flower and produce fruits, which birds eat and then deposit on other areas, causing buckthorn to grow in those areas.
Even the seeds themselves are very tough. Buckthorn seeds are viable for up to 5-7 years in the soil. You can kill a patch of buckthorn, but if you don't scour the area for seeds and monitor the area for new growth, the seeds can grow into new buckthorn just when you think you've killed it off and won the battle.
What should I do if buckthorn has invaded my property?
Simply put: remove it yourself or have it removed.
If the buckthorn plants are smaller than a pencil, you may simply pull it from the ground or spray it with a properly mixed foliar treatment of Garlon4, Impel, and 2,4-D.
If the diameter of the trunk is larger than a pencil you should use the "cut-stump method" Cut the buckthorn off, leaving approx. 3-4 inches of the trunk exposed, and spray the stump and surrounding bark with a mixture of Garlon4 and Impel Red. Attempting to pull buckthorn this large is not a good option, because many of the fibrous roots in the ground will remain intact. These roots will continue to grow and re-sprout into buckthorn plants in a very short amount of time.
Another method than can be useful is the "basal bark treatment" method (aka "basal stem treatment method"). Apply a mixture of Triclopyr ester (i.e., Garlon 4 or Pathfinder II) mixed with an oil diluent ( i.e. Impel Red, Bark Oil Blue, kerosene or diesel oil) using a low volume sprayer directly to the bark of buckthorn from the root collar up about 12-18 inches. This method works best on trunks less than 3 inches in diameter.
Warning: over-application of this mixture (i.e., over-spray and/or run-off) will greatly increase the odds of potential non-target injury to the surrounding desirable trees. The advantage to this method is that you can kill the buckthorn without having to remove the tree itself. This is often a method preferred by parks and other large parcels of land where removing the buckthorn entirely (i.e. using the cut-stump method) is simply cost prohibitive. The disadvantages of using the basal bark treatment method are that because you're leaving the tree intact, you're still minimizing the amount of sunlight allowed through its canopy of branches to the forests understory (thus aiding in shading-out future desirable growth). The potential for non-target injury is much greater when compared to the cut-stump method. It's also worth mentioning that the basal bark method has not been proven to be as effective when compared to using the cut-stump method (especially on larger buckthorn greater than 3'' in diameter). Hence the reason we prefer and encourage other to use the cut-stump method whenever possible.
There are other methods of removal such as Girdle herbicide application, Crown removal, and controlled burns. We won't go into these alternative methods because they are typically cost prohibitive and/or not as effective as the "tried and true" cut-stump method.
How long does removal usually take, and how much does it cost?
We typically charge $65.00 per man-hour, plus chemical & equipment fees (i.e. bobcat, wood chipper, etc.).
Removing buckthorn is an arduous process that is only effective when done methodically. Each buckthorn tree that is cut needs to be dragged over to a wood chipper, fed through the machine, and have its stump treated with a very potent herbicide that must be applied with precision (one can't simply "hose it down" without killing more than the buckthorn).
Because Buckthorn varies in size and density it is impossible to give an average amount of time (i.e. how long it would take 2 men to clear one acre of buckthorn). Hence the reason most companies work "by the hour". For larger projects consisting of several acres of land, a general rule of thumb is $900 per thousand square feet of infested forest.
We also replant trees and shrubbery that help strengthen the surrounding ecosystem. We typically replant the area immediately after we remove the buckthorn. Some people recommend waiting several weeks, but because we are so careful during the herbicide-application process, we have never had difficulty planting good healthy trees and shrubs immediately after removing and poisoning the existing buckthorn.
In fact, we recycle the shredded buckthorn and use it around the base of each new planting to help keep the weeds down and retain moisture. Though some people worry about the buckthorn seeds in the mulch growing into new buckthorn, we have not found this to be a problem: only a few seeds survive the wood chipper, whereas buckthorn typically springs up as a result of hundreds of thousands of seeds laying dormant in soil. In Layman's terms: The mulch snuffs out more dormant seeds in the soil that it does produce new growth as a result of a few seeds that may have survived the chipper/shredder.
We've found this "green" method of buckthorn removal to be the most resourceful and cost-effective. The shredded buckthorn serves a regenerative purpose, and the customer doesn't have to pay additional fees to have the buckthorn hauled off-site for disposal. Also, hauling the buckthorn off-site for disposal without being chipped only contributes to the spread of buckthorn-whereas killing it, chipping it, and reusing it on-site can turn blight into a blessing for the ecosystem. We like to think of it the Buckthorns way of "giving back" to the ecosystem it had a hand in destroying.
Is there a way I can prevent buckthorn from growing in the first place?
There is nothing you can do to "prevent" it other than remove it or have it removed as soon as you see it. That's why it's considered an invasive species. The best way to prevent buckthorn is simply to be able to identify it and remove it (or have it removed).
What kinds of chemicals are necessary to kill buckthorn?
A variety of chemicals are effective, when applied to the cut stumps of buckthorn trees or - in some cases - their bark.
Below is a chart that shows some of the common anti-buckthorn chemicals, as well as their suggested applications:
All the herbicides listed above are available under other brand names (with the same active ingredients), and are equally effective.
Always read the chemical labels, follow the instructions, and use the proper safety equipment. Chemicals like Garlon 4 can become volatile in temperatures above 85 degrees Fahrenheit, and can pose serious health risks if inhaled.
Of course, other plants will be damaged or killed if exposed to these chemicals. But because the proper way to apply these chemicals is to apply them directly to the buckthorn and only to the buckthorn, other, more welcome plants are unlikely to suffer as long as the chemicals are applied in a localized way.
You can eradicate relatively small buckthorn plants with what's called a foliar treatment - that is, applying the chemical mixture to the green leaves of the plant, rather than to the cut stump or the bark. You can make a foliar treatment by using a 1.5% solution of the active ingredient glyphosate (AKA "Roundup").
A warning: with a foliar treatment it's possible to damage surrounding plants, because you will need to spray the chemical mixture over the entire area of the plant. It's likely that more-welcome species of plants will be damaged. Obviously, this collateral damage is only a consideration if the small buckthorn plants are surrounded by other plants.
What should I do once the buckthorn has been removed?
It depends on where the buckthorn grew: on a patch of woods that you don't necessarily visit every day but that you want to protect, or on land that you live on or closely tend to.
In the first case-if the buckthorn grew in the woods-for roughly 5-7 years after the initial removal you'll want to kill any new buckthorn growth by using a foliar treatment (that is, an herbicide applied to the buckthorn leaves).
The best time to do this is in the fall. In Minnesota, around Halloween-time buckthorn is about the only thing in the woods that's still green. Because of this, it is very easy to identify in the woods. Also, because it is autumn, the buckthorn plants are pulling all their nutrients into their roots in order to prepare for winter. Applying an herbicide this time of year is very effective because the poison is quickly absorbed and pulled down into the root of the plant.
In the second case-if buckthorn is growing on property that you live on or otherwise tend closely-the best approach is a combination of annual foliar treatments along with planting and maintaining other more desirable plants. As tough and aggressive as buckthorn is, it can't grow as easily around well-developed plants, where it has to compete for nutrients and sunlight. The best way to deter-albeit not entirely prevent-buckthorn from recurring is to plant other foliage in its place once it's been eradicated. Do this and continue with foliar treatment every October and you'll be well on your way to reestablishing a healthy MN forest.
A few good examples of environmentally-friendly plants with which to replace Buckthorn include:
- High-bush cranberry (Viburnum trilobum);
- Nannyberry (Viburnum lentago);
- Chokecherry (Prunus virginiana);
- Grey dogwood (Cornus racemosa);
- Pagoda dogwood (Cornus alternifolia);
- American hazelnut (Corylus americana);
- Black chokeberry (Aronia melanocarpa);
- American hornbeam (Carpinus caroliniana ssp. Virginiana);
- Juneberry (Amelanchier laevis), and
- Northern White Cedar and Red Cedar
Other plants may also be good anti-Buckthorn measures; the above are just a few examples.
Further reading on buckthorn: