How invasive plants can damage property and infrastructure

By: Renee Sandelowsky and Helen Varekamp

Many of our readers are aware of the damage invasive plants can cause and the costs associated with eradication.

As a country, Canada has pledged to reduce the spread and introduction of invasive species by half by 2030.

Since gardening is the primary pathway for their introduction, everyone can take responsibility and provide support by choosing not to buy invasive plants, to remove them from our gardens and to learn more about their impacts.

This column, we focus on risks invasive plants pose to infrastructure, such as fire, erosion, drainage systems and property values.

Invasive plants such as Knotweed roots, Japanese Honeysuckle, Chinese Silvergrass, Callery Pear, and Yellow Flag Iris, damage property and infrastructure while increasing the risk of fire and erosion and even reducing property values.

Knotweed roots are so strong that they can damage pavement, building foundations and drainage systems by growing through existing cracks and expansion joints, forcing them wider over time, and potentially compromising structural integrity.

Their dieback in winter also leaves streambanks and slopes bare, increasing the risk of erosion.

Japanese Honeysuckle can smother groundcover vegetation, reducing root mass that holds soil in place and making slopes more prone to erosion.

Some invasive plants sold as ornamentals pose a fire hazard.

For example, Chinese Silvergrass forms dense, dry stands late in the season that can ignite easily. The same is true for Phragmites.

Callery Pear forms dense thorny thickets, has brittle branches prone to breakage, and produces foul-smelling flowers.

While in Canada, invasive plants are not yet widely recognised by the public as a property deterrent, some buyers may be discouraged by the cost and effort required to remove species such as Knotweed or Buckthorn once they understand the scale of the problem.

In the U.K. residents are legally required to disclose the presence of Knotweed on their property when selling.

Invasive plants can also damage green infrastructure, which is the vegetation and soils that naturally manage stormwater, filter pollutants, and maintain air quality, by displacing deep-rooted native plants, reducing soil stability and altering water flow and nutrient cycles.

Other invasives, such as Yellow Flag Iris, spread so rapidly and have such a dense root system that it may obstruct waterflow in drainage systems.

This is only a fraction of the documented impacts.

Whether or not this feels personally relevant, the evidence is clear that invasive plants from the horticultural trade impose significant costs on nature and on the economy.

As a gardener, please choose your plants wisely and consider becoming a supporter of the Canadian Coalition for Invasive Plant Regulation; it’s free.

Visit www.ccipr.ca for more information.

Renee Sandelowsky and Helen Varekamp are volunteers for the Canadian Coalition for Invasive Plant Regulation