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What NOT to plant in your garden - Invasive Plants in Ontario

Updated: May 31, 2023

Isn't it magical to be out in your garden and planning which plants you want to add? Perhaps you're starting with a blank canvas, or you inherited a piece of overgrown land and need to discover the fauna and flora underneath or you're simply redoing your existing garden. Whatever the reason, it's a good idea to study the names and features of invasive species before you accept a plant from a friend or purchase one at your local nursery. Not only do invasive plants disrupt the natural eco-system, they can clog up waterways, poison the soil for other plants and simply take over, creating a nightmare for biodiversity.


According to the Ontario Invasive Plant Council, invasive plants are classified as follows:

"Invasive species are plants, animals, and micro-organisms that are found outside of their natural range, and whose presence poses a threat to environmental health, the economy, or society (Government of Canada, 2004).


The Ontario Ministry of Resources and Forestry, in collaboration with Ontario non-profit organizations, is actively working to track and manage existing invasive species, while monitoring for the introduction of new species."


Unfortunately, some of these plants are readily available for purchase. Luckily, gardeners can help bring about a change by doing a bit of research before buying and planting an invasive plant. Bring it up in casual conversation with other gardeners and find out what they found invasive and how they were able to get rid of it!


A green bin of Waterloo Region Waste Collection
Waste Collection Waterloo Region

Be sure to discard any invasive plant in the green bin or tie it up in a black garbage bag until it's completely destroyed. If you put it in the garden waste or your home composter, it will just get redistributed into the environment and your yard!






Below is a list of invasive species and photos:


Ontario has a number of invasive plants that pose a threat to the native ecosystem. Here are some of the worst invasive plants in Ontario:

  1. Garlic Mustard: This plant can quickly dominate forest floors and has the ability to crowd out native plant species.

  2. Phragmites: Also known as common reed, Phragmites is a tall grass that can grow up to 5 meters high and can form dense stands that reduce biodiversity and interfere with water flow.

  3. Purple Loosestrife: This plant is known for its striking purple flowers, but it is highly invasive and can take over wetlands, crowding out native plants and disrupting the ecosystem.

  4. Japanese Knotweed: This plant can grow up to 3 meters tall and has an extensive root system that can damage building foundations and underground pipes.

  5. Giant Hogweed: This plant can grow up to 5 meters tall and its sap can cause severe skin burns and blisters. It can also outcompete native plants and disrupt the ecosystem.

Three more invasive plants that are rampantly spreading in Kitchener Waterloo:


Invasive periwinkle, also known as creeping myrtle or Vinca minor, is a ground cover plant that is native to Europe and was introduced to North America as an ornamental plant. While it is still commonly used as a landscaping plant, it has become invasive in many parts of North America, including Ontario.


Invasive periwinkle can form dense mats that outcompete native plants, particularly in woodland areas. The plant spreads through both vegetative reproduction (where pieces of the plant break off and root themselves) and by seed. Once established, it can be difficult to control, as the plant has a deep root system and is tolerant of a wide range of growing conditions.

To prevent the spread of invasive periwinkle, it's important to avoid planting it in natural areas and to remove any plants that have spread beyond the intended planting area. Hand-pulling or digging out the plants can be effective for small infestations, but larger infestations may require the use of herbicides or mechanical control methods. It's important to follow best practices for invasive plant control to avoid unintended harm to native plants and wildlife.


Invasive ground elder, also known as bishop's weed or goutweed, is a herbaceous perennial plant that is native to Europe and Asia. It was introduced to North America as an ornamental plant and has since become invasive in many areas, including Ontario.

Ground elder spreads rapidly through an extensive root system and can form dense patches that outcompete native plants. The plant also produces seeds, which can be spread by wind and wildlife, further contributing to its invasive potential. In addition, ground elder is difficult to eradicate due to its deep, persistent roots that can regenerate from small pieces left in the soil.


To control invasive ground elder, it is important to take a multi-pronged approach. Mechanical control methods such as hand-pulling and digging can be effective for small patches, but larger infestations may require the use of herbicides or repeated mowing to weaken the plants and prevent seed production. Additionally, preventing the spread of ground elder by removing any root fragments or plant material from garden waste and avoiding the spread of soil and contaminated equipment to other areas is important to prevent further spread of this invasive plant.


Invasive lily of the valley, also known as Convallaria majalis, is a perennial plant that is native to Europe and has been introduced to North America as an ornamental plant. This plant is now considered invasive in some parts of North America, including Ontario.

Lily of the valley spreads through rhizomes and can form dense mats that outcompete native plant species. The plant can also spread by seed, which can be dispersed by birds and other animals. In addition, lily of the valley contains toxic compounds that can be harmful to native plant and animal species.

To control invasive lily of the valley, it's important to remove any existing plants and their root systems, as well as to prevent further spread of the plant. Hand-pulling or digging can be effective for small infestations, but larger infestations may require the use of herbicides or mechanical control methods. It's important to follow best practices for invasive plant control to avoid unintended harm to native plants and wildlife. Additionally, avoiding planting lily of the valley in natural areas can help prevent its spread.


As gardeners, we have a responsibility to ensure the health of our gardens. By making informed choices, we're doing our part for the environment! Thank you, gardeners!!


Not sure what to plant? Here is a list of what to plant instead: Native Alternatives.


If you have any invasive species in your garden, please let us know in the comments. Feel free to share how it got there and how you're managing the spread.





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