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 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.

Another invasive plant that is spreading rapidly in the area 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 species, giant hogweed, has been in the media lately. It is a relatively new arrival in Northumberland. 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 3rd from 10:00am – 12:00pm. Pre-registration 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 native plants purchased from the 2nd Annual Port Hope Kinsmen Native Plant Sale on May 27th from 9:00am – 1:00pm at the GRCA on Hwy 28. You don’t want to miss out on the wide selection of trees, shrubs and flowers that will be available!