Written by Madeline Vang, Kroening Outdoor Ed. Intern
Common Buckthorn, also known as European Buckthorn or Rhamnus Cathartica, has been listed as a restricted noxious weed by the Minnesota Department of Agriculture. The sale, transport and movement of these trees are prohibited throughout the state. Common Buckthorn is an invasive species of trees native to northern Europe and Western Asia. These trees were brought to North America by Europeans to be used as hedges because of its hardiness and ability to survive in different soils. These trees grew and spread quickly, eventually crowding native species and taking their nutrients, making it an invasive species. They can grow to become 25 feet tall with a diameter of 10 inches. Their barks can be a grayish-brown color while their insides can be a yellow to pink color. The tree has small flowers with 4 yellow-greenish petals that begin to bloom in May. Their leaves are egg shaped, pointed at the end, with 3-5 veins.
Buckthorns are deciduous trees, meaning they lose their leaves every fall. However, their leaves stay green throughout mid-November. They lose their leaves about 58 days after other trees and get their leaves earlier than other trees. This is an issue since the leaves create shade for the native plants around them, blocking their sunlight. They outcompete native plants for nutrients and moisture. These trees can be harmful as they release chemicals into the soil to suppress the growth of the plants around them; this is called the Allelopathic Effect.
The soil under Buckthorn trees has higher nitrogen levels that encourages growth of disruptive species such as garlic mustard. These trees are hosts to pests such as crown rust fungus, alfalfa mosaic virus, soybean aphid, and oat crown rust. Buckthorn does not have any “natural controls” in North America, such as diseases or insects, to control their growth. They also contribute to erosion by shading the ground and outcompeting the plants that help the soil stay in place and moist. Native plants help stabilize the soil and absorb rainwater. Without them the rain washes soil and pollutants into bodies of water like the Mississippi River.
Common Buckthorn trees produce round berries, with 3-4 seeds, that grow in clusters and can cause laxative issues when consumed. The unripe berries are green while the ripe ones are a purple-black color. When consumed by humans, they can cause cramps and diarrhea. Buckthorn berries stay on their branches throughout mid-winter. Small critters like robins, red squirrels, mice, and cedar waxwings will eat these berries when other food supplies are low. However, areas with Buckthorns have a declining bird population due to their food sources and nesting sites declining because of the effects the berries have on them. When consumed, the berries will make the critters have diarrhea, become dehydrated, and eventually kill them. However if a bird does survive it will poop the seeds in another habitable area allowing a new tree to grow and allowing this invasive species to spread.
Buckthorn’s green leaves, green berries and bark can make a yellow dye. The bark can also be used to make a pink or rusty red dye. Green dye can be achieved by using the ripe purple-black berries, and blue dye can be made using only the skin of the berries. These berries and leaves can be frozen and the bark can be dried for later use. You can dye fabric or yarn with your homemade dye. In the past buckthorn berries were used to make ink and paint. The ink’s color can be a variation of yellow to green depending on the ripeness of the berries and how the colors were extracted.
Now that you know a little about this invasive tree species, what can you do about it? You can learn how to safely take down and dispose of these trees by volunteering at your local park, like North Mississippi Regional Park!
We are looking for volunteers at Kroening Nature Center in North Mississippi Regional Park. If you’re interested in taking down Common Buckthorn trees, making dyes with buckthorn, or helping out in any other ways reach out let us know at NorthMississippi@MinneapolisParks.org, 612-370-4844, or visit our nature center at 4900 N Mississippi Dr!