The invasion of garlic mustard and common buckthorn

By MPP Toby Barrett

The trillium is a symbol of spring – Ontario’s white floral emblem. But there’s another symbol of how invasives can dominate our landscape – the white blossom of garlic mustard. 

Like many invasives, garlic mustard is highly competitive and can force out natural species – like Ontario’s trillium. It produces an incredible number of seeds, can self-pollinate, and chemically inhibits the growth of other plants. 

This European herb was introduced to North America in the 1800s as food. It’s now running rampant provincewide. Not only found in woodlots, but also backyards.

This biennial grows low to the ground in the first year, with dark-green kidney shaped leaves with deep veins, usually in a round cluster. The second year, it sprouts vertically, growing on stalks with medium-green, triangular serrated leaves with small, white flowers.

Garlic mustard roots change soil chemistry and prevent other nearby species from growing. The roots’ chemicals are present in the leaves and deter herbivores from eating them. 

Landowners can make a difference by removing garlic mustard – even in backyards. Chemical herbicides or pulling the plants works for larger stands but don’t compost the plants as the seeds remain viable. 

Removed plants should be placed in black plastic or yard waste bags. Seal tightly and leave in direct sunlight for a week. Pulled plants, which have flowered, are still able to produce seeds, so plant pieces should be removed and either dried, burned or sent to landfill. 

Common buckthorn is another ornery invader. It’s a small shrub or tree native to Eurasia. It was introduced to North America in the 1880s as an ornamental shrub and was widely planted for fencerows and windbreaks. Since then it has spread aggressively throughout southern Ontario and other provinces. 

Buckthorn has smooth dark green leaves. It’s usually the first plant to leaf out in the spring and the last to drop its leaves in the fall. The branches of plants older than the first year end in a thorn, hence its name.

Common buckthorn produces copious seeds, creates dense stands and shades out native trees and shrubs. It can also host soybean aphids over the winter, impacting agriculture crops. For this reason, it’s listed as a noxious weed.

Smaller buckthorn plants can be pulled, but larger ones present a bigger challenge. One option is girdling the stem and applying herbicide. I use tractors with a chain or with a blade to remove larger buckthorn, and then I burn them. 

These are two of the newer, more aggressive invasive plants. Unfortunately, there are dozens- if not hundreds – of others. There are great online resources to learn about invasive plants such as

While local groups have organized events to tackle these invaders, COVD-19 restrictions have them on hold. That doesn’t mean individuals can’t make a difference on their own property. Also, if you find invasive species in the wild, contact the Invading Species Hotline at 1-800-563-7711 or visit the web site.

The province isn’t taking invasives lightly. Ontario is the only Canadian jurisdiction that has standalone invasive species legislation. The province recently posted a proposal to the Environmental Registry of Ontario to add 13 more species to the act. These include three types of knotweed, wild pigs and other invasives. These changes are still under consideration.

Toby Barrett is the MPP for Haldimand-Norfolk.