Common Buckthorn

Leaves: Buckthorn leaves are opposite to sub–opposite, occasionally alternate. The leaves are sharp, pointed, curved, or folded and have somewhat finely-rounded teeth.  Leaves have 3-5 strongly curvy veins per side with obvious/strong on the underside, arching towards the tip of the leaf. 

Flowers: Buckthorn flowers are a greenish-yellow color that are roughly 6 mm across on short threadlike stalks in dense clusters. They usually appear in early June with 4 stamens, 4 petals, and 4 sepals.

Fruit: Buckthorn fruit is black when mature and  green when immature, with dense clusters in leaf axils. Fruits have 3-4 seeds with deep narrow grooves on the back.

Bud: Buckthorn buds are scaly, almost black, and lie close to twig. Some dwarf shoots end in a thorn, opposite, sometimes alternate.

Bark: Buckthorn bark is greyish-brown and has prominent small lenticels. The bark is smooth and shiny when young and rough and textured when mature. The under layer is yellow-green and the heartwood is orange 

Branchlets: Terminal spine, no hairs. 

Form: Shrub or tree.

Size: 6-7 m in height and 25 cm in diameter. 

Common Buckthorn is native to Europe and is also known as European Buckthorn. In Canada, it is found from Nova Scotia to Saskatchewan. It was likely introduced around the 1880s, becoming widespread in the early 1900s. This species was often used in hedgerows and windbreaks, and was widely planted across the country. Common buckthorn is of concern to the agricultural community because it can host oat crown rust and soybean aphid, both of which reduce crop yields.

Common buckthorn berries are a common food for birds and the laxative properties of the seeds ensure they are spread widely and rapidly. Seedlings will begin to sprout under perch trees, and along fence lines and woodland edges. The seeds are also long-lived; they remain viable for five years and will rapidly colonize a site if space becomes available. Under conditions of full sun, favourable soil conditions (especially disturbed soils) and no competition, common buckthorn can mature and produce seed in a few years.

Distribution Map provided by EDDMapS

Impacts to biodiversity 

Common buckthorn can harm biodiversity in a number of ways, affecting soil quality, plant communities, and wildlife. It can change the nitrogen composition of soil, making it harder for other species to survive. These changes can have long-lasting effects even after common buckthorn has been removed. For example, native species such as chokecherry and pin cherry that have fruits that are beneficial to wildlife (i.e. not laxative like common buckthorn) may not survive even in the right conditions, due to soil changes. 

Common buckthorn seems to have a direct impact on understory plant communities and vegetation types, though no formal studies have been completed. There may be several reasons for lower numbers of native plant species in an area with common buckthorn, such as preferential deer browse and alterations in the soil composition and leaf layer caused by non-native earthworm populations. 

Common buckthorn may also encourage non-native earthworm establishment, which facilitates the destruction of leaf layers. Sites invaded by common buckthorn often show a lower species richness count and a higher concentration of weedy and exotic species, including invasive honeysuckle species (Lonicera spp). 

Common buckthorn has been shown to negatively affect some native songbird populations. Robins (Turdus migratorius) nesting in buckthorn are more susceptible to predators because of the low branch heights and lack of protective thorns (like those found on hawthorns and native rose species). The berries are eaten by thrushes (Turdidae), waxwings (Bombycilla), white-throated sparrows (Zonotrichia albicollis), jays (Corvidae) and small mammals. 

Impacts to Forestry

Land managers of wooded or open areas in southern Ontario are likely familiar with common buckthorn due to its aggressive spread by seed and prolific growth. 

Common buckthorn forms dense, even-aged stands that can tolerate shade and suppress other vegetation because of its long growing season. The growth of hundreds of buckthorn seedlings across the forest floor prevents other species, including native plants, from growing and surviving. Its greatest impact can be in somewhat disturbed sites, especially if in full sun. 

Once established on the edge of a forest, common buckthorn will spread into the interior. In southern Ontario, common buckthorn is found along forest edges and as a dominant part of the forest understory. It aggressively invades hardwood (deciduous) and softwood (coniferous) forests and can harm the surrounding soil similarly to aggressive allelopathic invaders such as garlic mustard (Alliaria petiolata). 

In North America, common buckthorn develops its leaves weeks before native species and loses them weeks after, effectively outcompeting native species for sunlight. These traits make it particularly harmful to hardwood forests and make it difficult for land managers to promote healthy forest growth and succession.

Impacts to Recreation

Common buckthorn can inhibit recreational activities in areas where it has become established. Its dense stands can make it difficult to walk along established trails. Common buckthorn also harms the aesthetic value of natural areas by reducing the abundance and variety of native species such as wildflowers.

Mechanical Control

Pulling: When the soil is moist, small plants up to 1 m (3 ft) in height can be pulled.  Larger plants can be dug out or pulled out using a weed wrench tool. Resprouting can occur unless all the roots are removed or other measures like fire or chemical control are used. Resprouting can worsen the problem dramatically. If pulling takes place in the fall, care should be taken to remove and contain branches with berries prior to pulling. Because of the thorns, it is recommended that volunteers or staff wear personal protective equipment.

Benefits of pulling in the fall/winter season (before the ground freezes) include the following:

• Leaves stay green longer and remain on the stem longer than our native trees and shrubs. This makes identification easier and reduces the potential of pulling look-alike species.
• Most of the ground vegetation has gone dormant at this time, reducing the disturbance to surrounding plants that may arise while pulling shrubs and walking through the site.

Cutting/girdling: Cutting or girdling (a cut groove down to the heartwood all the way around the stem) are also feasible control options. However, herbicide must be applied to fresh stumps or girdled areas to prevent resprouting. A precise application of herbicide from a small hand-pump bottle can be done at any time of the year, although late spring/early summer is the most effective time.

Girdling can weaken larger common buckthorn shrubs that can’t be pulled by hand or by mechanical means. This makes the shrub easier to remove mechanically the following year. Cutting the shrub down to a stump will cause sprouting and make stump removal very difficult. Sprouting will still occur with girdling but won’t be as vigorous as with cutting. Over time (1-2 years, girdling may need to be repeated after the first year) the canopy will begin to die, the roots will die back, and the shrub will become easier to pull out. When girdling, the band should be at least 3” wide to prevent wound closure and recovery of the shrub.

Mowing: Mowing will reduce stem numbers and vigour, and will eventually kill off most seedlings. It needs to be carried out in early and late summer for at least 2–3 consecutive years and is recommended for stems that are less than 2 years old. Mowing will also prevent growth of native vegetation, so this control method should only be used in areas with dense buckthorn seedlings where restoration will occur.

Chemical Control

See Buckthorn Best Management Practice (below)