Wellington County – Summer is in full swing with fine flowers blooming.
Orange daylilies fill the ditches. The white flowers of lily-of-the-valley send sweet scents into the air. Variegated gout spreads through gardens and forests. Creeping purple bellflowers sway in the wind leaving glistening flower leaves on the ground.
Although their beauty is tempting, experts recommend preventing these plants pronto.
Invasive and harmful
Why? It is invasive, meaning that it is harmful to the environment, the economy, and/or society, including human health.
Invasive species replace native plants that are food sources for insects and animals. They affect crop production by invading farm fields and destroying infrastructure such as buildings, sidewalks, and roads.
Most invasive plants have been introduced intentionally, such as ornamental flowers and agricultural crops. But they escape from gardens and agricultural fields, spreading through forests and wetlands.
“We need to wake up to the potential impact of invasive plants,” said Cathy Cavsalis, master gardener and founder of the Canadian Invasive Plant Regulatory Alliance.
She said it is common for people to feel that the plants in their gardens are not a problem because they are under control. But the seeds spread far and wide, invading natural spaces without the knowledge of gardeners.
She said, “People don’t know.”
“Invasive plants replace all native plants,” Kavasalis said, reducing biodiversity and disrupting the essential food web.
“There is a lot at stake with the loss of local diversity.”
Many invasives are not food for native insects or birds, so when they replace native plants their numbers decline.
The networks of life collapse
“Insects are decreasing by 9 percent per decade,” she said, referring to an April 2020 analysis in the journal Sciences.
North America has lost 2.9 billion birds since 1970, according to another study published in Sciences.
“This is one in four goldfinches,” Kavasalis said.
“It’s all part of the big picture that I think we as gardeners didn’t recognize until recently.”
The economic impact is significant, with invasive plants costing Canadian agriculture an estimated $2.2 billion annually, according to Environment Canada.
The impact is also cultural and spiritual, Kavasalis said, particularly when invasions displace plants important to the indigenous population.
Rosemary Fernandez-Walker, master gardener and founder of the Guelph Gardeners Facebook group, said she wished more people knew about invasive plants, “and that they negatively affect the growth of other plants and the environment as well.”
People are spreading awareness about invasive plants in the Fernandes-Walker Facebook group, which has nearly 5,000 members and can be found at www.facebook.com/groups/guelphgardeners.
“Diversity is key to the survival of all species, including humans,” said Kathryn Goddard, co-founder of Guelph’s Tree Trust and long-term member of the North American Native Plant Society. She recommends people “create habitats instead of gardens.”
Cavasalis, Fernandez-Walker, and Goddard all acknowledged the rise of invasive species before they knew not to.
“Many of us were late for this match,” Kavasalis said.
“I propagated a lot of these invasive plants because they were so easy to grow. In my later years, I’m trying to make some compensation and right some of the damage we gardeners have done…so that my grandchildren and other great-grandchildren will not bear this terrible burden we have left behind.”
Removal of gaseous materials
“There are no simple solutions” to removing invasive plants — “that’s why they are invasive,” Kavasalis said. If they were easy to remove, they wouldn’t be on the list of invasive plants.
“They can all be removed, it just takes patience and perseverance. And if you can’t get rid of it, just make sure it can’t multiply” by mowing it and containing it with barriers in soil, she recommends.
“The Ontario Invasive Plants Council (OIPC) has great best practices” for different plants, Kavasalis said, adding that “there is no one-size-fits-all approach.
Other best practices and resources are available online at www.ontarioinvasiveplants.ca/resources.
“Some you can solarize, some you can dig up, some you can mow. For some, you have to use herbicides,” she said—but for some gardeners, like Goddard, herbicides are never the answer.
When removal isn’t possible, mowing or weeding is better than nothing, Goddard said, because it limits spread by preventing the plant from going to seed.
Many invasive plants are sold in Ontario nurseries, Kavasalis said, because “we don’t have a very good system at banning the sale of this stuff.”
The federal government takes the issue to the provinces, the counties pass it to the municipalities, and the municipalities pass it to the homeowners, she said, meaning the problem is left to those who are “least able to tackle the big picture.”
Kavassalis started the Canadian Invasive Plant Regulatory Coalition to raise awareness and advocate for stronger government regulation, such as labeling invasive plants and banning the sale.
“We need to put in place a system that helps the public,” she said. That way, “gardeners can buy their plants with confidence and they won’t do any harm.”
She said Canada should implement a risk assessment system before importing plants, as did Australia and New Zealand.
Details about Canadian Invasive Plant Coalition regulation are available at www.ccipr.ca.