As the late summer wraps up and yields to the coming of autumn, we too begin to transition into a new part of our year—battlin’ buckthorn season!

Ok, so it’s technically woody invasive species treatment season, but in our neck of the woods, that means a lot of buckthorn treatment. September-November is prime buckthorn treatment season, so today we are going to break down buckthorn, and how and why we manage it during this seasonal transition.

What is Buckthorn?

Common and Glossy buckthorn (Rhamnus cathartica, Rhamnus frangula), commonly referred to as simply buckthorn, is an ornamental shrub native to Europe and western Asia. Originally introduced to the US as an ornamental hedge plant, it escaped into the wild and began to take over natural areas. It is commonly found throughout southern and central Minnesota in forests, encroaching prairies, along roadways, and within backyards. You’ve likely seen buckthorn, even if you don’t realize it.

Buckthorn is problematic because of the extent of its growth, and the ways it alters soil properties. Buckthorn is successful at growing in a lot of different environments. It tolerates both sun and shade, as well as a variety of soil types and moisture levels. There are few places where buckthorn won’t grow well. When buckthorn invades a place, it creates dense monocultures, crowding out native plants. The density of growth outcompetes native shrubs and tree seedlings. It can over crowd native mature trees, robbing them of nutrients and growing space. Finally, the density of the growth overshades native ground covers and understory plants, creating bare soil conditions beneath buckthorn groves. This can contribute to soil erosion since there is no ground cover protecting the soil.   

Buckthorn leaves stay on the plants for a long time—it is often the first plant to green out in the spring, and the last to stay green in the fall. These leaves have a high nitrogen content, so when buckthorn does drop its leaves, their decomposition adds excessive nitrogen to the soil. This can increase soil pH, improving growing conditions for more buckthorn, while limiting them for other plants. Furthermore, buckthorn is a host plant for crown rust fungus and Asian soybean aphid, to agricultural pests. Basically, buckthorn is bad news for natural areas and agricultural areas.

Unfortunately, buckthorn is often propagated, tolerated, or desired for the privacy cover it provides. Its fast, dense growth can be applauded for providing screening and cover—and this is often how it has been used in landscaping. However, there are many native shrub species that work just as well as a privacy screen. So, if you want to keep your privacy, don’t think keeping your buckthorn around is the only solution.

Why Target Buckthorn Now?

We’re of the opinion that buckthorn should be removed wherever it grows, and replaced with native plants. At the very least native plants should be given a fair advantage to grow (which means controlling buckthorn growth). Which brings us to our upcoming battlin’ buckthorn season.

We focus on buckthorn (and other woody invasive species) removal and treatment in the autumn months. There are a couple of reasons for this, both based in ecological principals. First, September-November is when plants in the north start to turn color and drop their leaves. This occurs because the plants are taking all the nutrients, food, and energy in their leaves and pulling them down into their roots to store for the winter. This translocation, or movement within, of the energy in the plant is an important process that we take advantage of for our management. Applying herbicide to the leaves or stem of buckthorn during this time means that the herbicide is pulled down into the roots along with the energy stores. This gives the herbicide a better chance of successfully killing the roots of the buckthorn, preventing it from resprouting. Simply cutting or top killing the plant will not fully kill buckthorn, as there is usually enough life in the roots to allow the plant to resprout. So, we take advantage of the natural movement of nutrients within plants at this time of year to assist with fully killing the root systems.

This process of translocating, or going dormant for the winter, is prolonged for buckthorn compared to many native plants. This means that buckthorn keeps its leaves for a long time through the autumn. This is the second reason we focus buckthorn treatment for this time of year. We can treat buckthorn with limited risk of damaging native plants which have already moved the bulk of their nutrients into their root systems, or lost their leaves completely.

Buckthorn Control

For these reasons, we spend the bulk of our time from September through November treating buckthorn. We use a number of different techniques for managing buckthorn, depending on the site conditions and size and density of the buckthorn. The three most common treatments are foliar spraying, cut and stump treat, and forestry mowing.

Foliar spraying involves applying a selective herbicide to the leaves of smaller buckthorn plants. The herbicide is absorbed into the plants and transported down into the roots. This method is best used for buckthorn that are under about 3’ tall. It is commonly used following mechanical removal to treat new seedlings and resprouts.

Cut and stump treatment is a combination of mechanical removal and herbicide application. We cut the buckthorn at the ground level using brushsaws or chainsaws, then apply herbicide to the stump. Cutting the buckthorn clears out the dense monocultures it creates, and can limit the spread of berries and seeds. The herbicide applied to the stump absorbs into the plant and is transported to the roots, helping kill the root system and prevent it from resprouting. This method is best for larger sized buckthorn of at least ½ inch diameter or over 3’ tall.

Forestry mowing is growing in popularity as a buckthorn management method. It utilizes a large mowing drum attached to a bobcat or skid steer. The drum runs over buckthorn, shredding the stump and mulching up the stem and branches. This instantly clears the physical buckthorn growth, and can help limit the spread of berries and seed. The shredded stems are more difficult for the plant to seal, and the roots may expend all their remaining energy trying to recover from the shredded damage. Basically, this means that forestry mowed stems don’t always require herbicide to kill the plant, which can reduce the amount of herbicide applied to a site. Forestry mowing is best used on larger acreages with dense buckthorn and little native species growth.

There are a few other methods for removing buckthorn that are common in smaller areas such as yards. The most common is to pull up buckthorn from the roots using your bare hands or a weed wrench. This method is physical intensive, but removes the possibility of resprouting by completely removing the roots of the plant. Many people also prefer this method because it doesn’t use herbicide. However, uprooting large buckthorn plants disrupts a lot of soil, and leaves large open areas of disturbed soil. This can encourage germination of buckthorn seeds in the soil, or other invasive weeds. If you are physically uprooting buckthorn plants, make sure to restore the disturbed soil. It’s also best to have some native seeds or plants to put in place of the removed buckthorn to discourage other weeds from moving in.

Cutting or mowing is also a common treatment for buckthorn in urban areas. While mowing will knock down the stems of buckthorn and prevent them from going to seed, it is not likely to kill buckthorn. To seriously damage buckthorn populations, mowing needs to occur multiple times in the year—in the early spring when buckthorn is starting to grow, in the mid-summer right before buckthorn goes to seed, in the late summer right as buckthorn starts going dormant, and sometimes one more right as winter sets in. This may not do more than control the buckthorn population, but can be an option if no other treatment is possible.

Finally, buckthorn can be susceptible to burning when it is still a small seedling. The roots of more mature buckthorn are often too resilient to be fully killed by fire, so prescribed burning is best when buckthorn growth is young and small. Burning during the hot part of late summer (August-September) can help create hot enough fire conditions to kill buckthorn growth. Prescribed fire should only be used in certain conditions, and by trained professionals like NRP.

So, if you have buckthorn on your property (chances are you do), consider one of the above management methods to keep it in check. It may seem like a lot of work, and a constant uphill battle, but your trees, native plants, and soil will thank you for it. If buckthorn removal seems overwhelming on your own, call us in! Battling buckthorn is something we do best!

We’re approaching buckthorn removal season, so now is a great time to contact us for a consultation. We can help design and implement a buckthorn removal and control plan best suited for your property and needs.