As you hunker down next to your fireplace during the cooler days of winter or when you partake in festive events, you may be listening to Christmas carols, including traditional pieces such as “Deck the Halls with Boughs of Holly”and “The Holly and the Ivy.” But wait. Holly and ivy? Are these invasive plants? Yes, even during the festive season I can manage to bring you woeful stories of invasive plants.
The green and red colours of holly and ivy are traditionally associated with Christmas, and decorating homes with wreaths of fir and cedar boughs, and sprigs of holly, ivy and mistletoe, are age-old Christmas customs. English holly (Ilex aquifolium), with its shiny green, prickly leaves and clusters of red berries, is especially symbolic of the holidays. Holly is a large, evergreen shrub that can grow to the height of a small tree, up to 13 metres (43 feet). Plants are typically either male or female, and it is the female plant that produces the scarlet berries. In order to produce berries, female plants must grow in quite close proximity to male plants. Holly bark is smooth and grey, and the wood is white and hard with a very even grain. Valued by wood turners, it has been used for inlay work, chess pieces and black piano keys.
Originally from Eurasia and northern Africa, English holly was introduced to North America as an ornamental shrub. Holly is a hardy plant that can withstand a variety of conditions. It prefers mild winters, and thrives in many locations throughout the Pacific Northwest. It is particularly a problem in North Vancouver and on portions of Vancouver Island where it has escaped from urban gardens and spread into woodlands and parks. In these locations, holly can dominate the tall shrub layer, creating a deep shade difficult for some native species to grow in. Many groups, such as the Invasive Plant Council of Metro Vancouver, are actively involved in controlling this invader.
English holly is considered invasive in B.C., Washington, Oregon, California and Hawaii, as well as Australia and New Zealand. A few years ago it was included on the “top 13” list of the most unwanted horticulture plants in BC. Similarly in Washington State, a recent survey of invasive plants in all the public forests in the Seattle area concluded that English holly was the fourth most abundant invasive plant, after Himalayan blackberry, Scotch broom and English ivy.
While English holly does grow in our region, I do not anticipate it to ever become the problem that it presents at the coast. However, as with so many other ornamental plants that are potentially invasive, it’s important to consider where you live and whether your property borders a natural park where holly could get a foothold. And while it is unquestionably an attractive plant, I would strongly encourage the planting of alternate species whenever possible. Consider other varieties of holly that are not considered invasive or better yet, plant Oregon-grape (Mahonia aquifolium), an equally beautiful native plant that produces clusters of showy yellow flowers in the spring, followed by blue berries in the late summer. If you do choose to grow English holly, consider cutting off the dead flowers, seedpods and berries to reduce the opportunities for this plant to spread. While unpalatable to most wildlife, there are a few bird species that do eat holly berries, and disperse the seeds in nearby natural habitats.
For further information on invasive plants in the Okanagan-Similkameen check out our website at www.sosips.ca or contact the Invasive Plant Program Coordinator, Lisa Scott, at 250-404-0115 or email her at firstname.lastname@example.org
Contributed by Lisa Scott