Despite the popular Christmas lyrics, please don’t deck your halls with boughs of holly. As with many invasive species that have naturalized across the Pacific Northwest, English holly was brought here in the mid 1800s to be planted in the gardens of settlers as a familiar piece of home. More recently, English holly was farmed for its commercial value during the Christmas season. As recently as 50 years ago, many farms across Vancouver Island were farming holly and some still do to this day.
What Is English Holly?
English holly is a slow growing evergreen shrub renowned for its dark green, glossy foliage and bright red berries. Plants can reach 15-50 feet tall and grow 15 feet wide. Easily adapted to both sun and shade, holly can be found in a variety of habitats including coniferous and deciduous forest, wetlands, and residential areas.
In the winter, female holly trees produce the bright red berries we know so well. Each berry contains around 3-4 seeds and on any given year a female holly tree will produce close to 120,000 seeds. In addition, English holly can reproduce vegetatively, meaning it can produce suckers from its roots as well as root branches and stems that meet the soil. In the instance a holly tree is cut down, if the stumps are left uncontrolled the holly tree will resprout.
How Does It Affect The Ecosystem?
Though holly trees are relatively slow to grow, and can take years to mature, they can live for hundreds of years and their growth and reproductive rates increase exponentially as they get older. Unlike sun-loving invasive species such as Scotch broom that are limited to roadsides and open-canopy ecosystem types, shade tolerant species like English holly and daphne will happily spread across Mayne Island. Due to the adaptability of English holly, this species can easily and quickly change the composition of an ecosystem. English holly has deep and aggressive root systems that can outcompete native species for water and other nutrients. In fact, holly is a notorious water hog and can leave surrounding native species without sufficient access to water. This is important to note as native plants on Mayne already have limited access to water in the summer and a species like English holly can exacerbate water availability during droughts. Additionally, holly can form dense thickets that shade out the native understory and allows the holly to take hold and spread. Holly seeds are spread by birds. The berries are toxic to humans and pets but are a tasty snack to our feathered friends where the seeds are spread through their feces.
What Can We Do To Control It?
To manage this species, there are two main methods of control: manual and chemical. If the English holly individuals encountered are young, often they can be removed by hand pulling or digging out the root systems. An annual survey of your property to pull out any young plants you find is the most effective method for managing this species. As the trees get larger, other methods such as using loppers to trim the branches and then shovels to dig out the tree can be effective, but once the trees are too large to dig by hand the management methods are limited to digging with large machinery or application of a systemic herbicide.
Chemical control should be handled by professionals and involves cutting the tree down, followed by herbicide application to the exposed stump. This method can be effective to prevent resprouting but often requires repeat herbicide applications. Untreated stumps will re-grow stems from the base, and often suckers will sprout up from roots all around the stump, creating a large thicket where the single tree once stood.
For both methods, it is important to not put any berries in the compost as it can contaminate the soil and further the spread of the plants.
Finally, the most effective control of English holly, as with all invasive species, is to not plant these species in your garden in the first place. Instead, try planting native species such as tall Oregon grape for similar leaf texture and beautiful blue berries, red elderberry with, as the name suggests, bright red berries, or evergreen huckleberry.