Invasive Plants Pose Problems

Invasive plants are species that have been accidentally or deliberately introduced to an area outside of their normal range, and which due to their rapid spread, become a threat to the environment, the economy or to human health. One invasive plant that has spread rapidly into Northumberland County is garlic mustard. This biennial begins its first year as a basal rosette of kidney-shaped leaves that remain green under the snow, which gives them a head start in the spring. By early May, the plant has sent up a stem topped with numerous small white four-petal flowers. Later, tiny seeds cling to wet clothes, boots, tires and animal fur, and within a few years a single plant becomes thousands, spreading through the forest and threatening native wildflowers such as trilliums, trout lilies, hepatica, etc.

Another invasive plant that is quickly spreading in the Northumberland area is pale swallowwort, also known as dog-strangling vine. This relative of the milkweed, with its tiny brown star-shaped flowers and slender seed pods, doesn’t really strangle dogs; however, its spread can become so extensive that it chokes out native species and even prevents young trees from growing.

Giant Hogweed is being seen more and more across the Ganaraska watershed. This spectacular plant grows up to 5 metres tall and sports huge white flat-topped flowers. Giant hogweed produces a toxic sap; when this contacts skin and is exposed to the sun, severe blistering can occur. In the same family and only slightly less toxic is another recent arrival, wild parsnip. This plant grows about a metre in height and has yellow flat-topped flowers by mid-summer. Locally, it is spreading rapidly along roadsides, trails and in disturbed areas where it poses a real health threat to those who don’t recognize and avoid it.

Dive into species identification and best management practices at the Ganaraska Region Conservation Authority (GRCA) Invasive Species Walk on Saturday, June 2nd from 10:00am – 12:00pm. Pre-registration for this free event is required through the GRCA at 905.885.8173. If you cannot attend the event and want to learn more about local invasive plants, contact the GRCA or visit

Stay clear of invasives in your garden this year by planting only native plants. When you visit your local nursery or garden centre, make sure you know what you are purchasing. Visit to learn more about invasive plants.

Interested in a rain barrel for your garden? The GRCA is offering pre-sales with order pick-ups at the GRCA head office on May 26th from 8:00am – 12:00pm. Order your rain barrel today! For further information, contact or 905.885.8173

Written By: Ken Towle, GRCA Terrestrial Ecologist