Phragmites: The Invasive Grass Taking Over Ontario Shorelines
Drive along almost any stretch of Highway 21 between Grand Bend and Goderich, and you will see them: towering walls of straw-coloured grass, three to five metres tall, lining the ditches and creeping toward the lake. Phragmites australis, the European common reed, has become the most aggressive invasive plant species in Ontario's coastal wetlands. And the problem is getting worse every year.
The Ontario Invasive Species Centre has called Phragmites "Canada's worst invasive plant." That label is not hyperbole. This single grass species is responsible for displacing dozens of native wetland plants, reducing biodiversity in marshes that once supported everything from Blanding's turtles to least bitterns. Along the shores of Lake Huron, Lake Erie, and Georgian Bay, vast monocultures of Phragmites have replaced what were once complex, multi-layered wetland communities.
How It Spreads
Phragmites spreads through two mechanisms, both ruthlessly effective. Underground rhizomes extend horizontally through the soil at rates of up to two metres per year, forming dense mats that crowd out competing root systems. Each rhizome node can produce a new shoot, meaning a single clump can colonize a football field's worth of wetland in under a decade. The plant also produces enormous seed heads, each carrying up to 2,000 seeds that travel on the wind or float downstream to establish new colonies.
Road construction and drainage ditches have been among the plant's greatest allies. Disturbed roadsides provide the bare, moist soil that Phragmites seeds need to germinate, and highway corridors act as migration routes connecting one wetland to the next. Once established along a ditch, the grass spreads into adjacent marshes, lakeshores, and river floodplains with alarming speed.
The native subspecies of Phragmites, Phragmites australis subsp. americanus, does occur in Ontario. It grows in scattered, modest clumps and coexists with other wetland plants. The invasive European strain, by contrast, forms dense stands so thick that nothing else survives beneath them. Telling the two apart requires close inspection of stem colour, leaf sheath characteristics, and growth pattern. Conservation authorities across the province have trained staff and volunteers to identify and report the invasive strain through programs like Ontario's invasive species reporting portal.
The Ecological Toll
When Phragmites takes hold of a shoreline or wetland, the ecological consequences cascade through the entire food web. Dense stands eliminate the open water and mudflat habitat that shorebirds need for foraging. Waterfowl nesting habitat shrinks as plant diversity collapses. Fish spawning areas along lakeshores lose the varied vegetation structure that young fish rely on for shelter, a concern explored in depth in our look at why protecting spawning habitat should be a local priority.
The plant also changes the physical characteristics of the wetland itself. Phragmites stands trap sediment at higher rates than native vegetation, gradually raising the ground level and converting wet marsh to dry land. The thick litter layer that accumulates beneath the stems decomposes slowly, further altering soil chemistry. Some researchers have documented Phragmites-dominated wetlands losing their water-filtering function, the very ecosystem service that makes coastal marshes so valuable in protecting water quality.
What Communities Are Doing
Control efforts have intensified across Ontario over the past decade. The most effective approach combines mechanical removal with targeted herbicide application. Crews cut the stands in late summer, then apply glyphosate-based herbicide to the cut stems before regrowth begins. In sensitive areas near water, aquatic-approved herbicides are used under strict permits from the Ontario Ministry of Natural Resources and Forestry.
Along the southeast shore of Lake Huron, the Ausable Bayfield Conservation Authority has been running coordinated Phragmites removal since 2014. Their program, one of the largest community-based efforts in the province, has treated hundreds of hectares along the shoreline. Volunteers play a central role, cutting stems by hand in areas where machinery cannot operate. Similar citizen science and volunteer monitoring programs have emerged across the Great Lakes basin.
Some municipalities have begun incorporating Phragmites management into their road maintenance budgets, recognizing that ditches serve as the primary vectors for spread. The Town of Wasaga Beach and the Municipality of Lambton Shores both fund annual mowing and herbicide programs for roadside Phragmites stands, treating the problem as infrastructure maintenance rather than purely an environmental concern.
Prevention Remains the Best Strategy
For lakefront property owners, early detection is critical. A single Phragmites shoot appearing in a garden or along a shoreline should be treated immediately, before rhizomes have a chance to establish. Pulling young plants by hand can work if the entire root system is removed, though even a small fragment left behind can regenerate. Property owners who maintain healthy riparian buffer zones with established native vegetation are less likely to see Phragmites establish, since the invasive grass struggles to compete in areas where dense native root networks already occupy the soil.
Planting native shoreline species in disturbed areas before Phragmites can colonize them is another effective preventive measure. Species like blue-joint grass (Calamagrostis canadensis) and lake sedge (Carex lacustris) can fill the same ecological niche without the destructive tendencies of their European cousin.
The fight against Phragmites is not one that any single property owner, municipality, or conservation authority can win alone. The plant's ability to spread across property lines and jurisdictional boundaries demands coordinated, sustained action. But as communities along Ontario's shorelines have demonstrated, organized efforts can reclaim ground from even the most tenacious invader. The alternative, surrendering thousands of hectares of coastal wetland to a single invasive grass, is simply not acceptable.
