Managing invasive plants

If you see the following plants on trails, parks or natural areas, please send us a photo and the location so we can investigate:

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How we manage invasive plants on City property

We use machinery and herbicide to remove giant hogweed, dog-strangling vine, Japanese knotweed and buckthorn from parks and natural areas. Manual removal alone is not always effective. We sometimes use herbicides to minimize disruption to surrounding plants and wildlife and prevent invasive plants from growing back.

The City uses Garlon™ RTU to control buckthorn, and Arsenal® to control dog strangling vine.

These products are registered for use in Canada and have been tested to ensure minimal risks to human health and the environment. Licensed applicators use targeted application, so we use as little as possible, and protect surrounding plants and wildlife.

Learn more about registered herbicides from Canadian Pest Management Regulatory Agency.

When the City is confident invasive plants are under control, we rehabilitate natural areas using native trees, shrubs and groundcover.

Do not touch giant hogweed

The sap of giant hogweed is dangerous to the skin, causing inflammation, burns and possible blindness if it gets in your eyes. Giant hogweed is an invasive plant originally from Asia.

  • Often mistaken for Queen Anne’s lace, cow parsnip and angelica; giant hogweed is much larger.
  • Tall, thick stem with reddish spots that stand 10 to 15 feet high.
  • Umbrella-shaped white flower head with a flat top.
Green plant with tall, thick stem with reddish spots that stands 10 to 15 feet high

How to remove giant hogweed from your property

The safest way to get rid of giant hogweed is to call a professional service. If you must remove it yourself:

  • Wear protective clothing including gloves, pants, long sleeves, eye protection, raincoat, and boots.
  • Remove flower heads to prevent seeds from growing
  • Cut plant roots 3-5 inches below the soil.
  • Seal it in two layers of plastic garbage bags and put it in your grey waste cart. Do not put it in your compost, green cart or bagged yard waste.
  • Wash the clothes you wore during removal.
  • Watch for any new growth and remove as needed.

Dog-strangling vine

    • It grows one to two metres high, coiling around other plants and trees.
    • In June, it has pink or purple star-shaped flowers with five petals bloom.
    • In late summer, it has bean-shaped pods four-seven centimetres long that open to release feathery white seeds.
    • Its leaves are shiny, yellow-green and dark green in the shape of ovals with a pointy tip.

Photo by R. A. Nonenmacher

How to remove dog-strangling vine from your property

  • Cut at the base.
  • Put it in the grey waste cart. Do not put it in your compost, green cart or bagged yard waste
  • Do not let it flower or seed.

Dog-strangling vine is an invasive species from Europe that is spreading rapidly throughout Ontario. This plant species smothers native plants and young trees which reduces habitat for birds, pollinators, and insects. It also increases wildlife grazing on native species.


Common buckthorn

  • Shrub grows up to 7.6 metres (25 feet) tall.
  • Outer bark is dark gray, inner bark is orange.
  • Twigs are usually tipped with a sharp thorn.
  • Flowers are yellow-green with four petals.
  • Fruit are purple to black and contain 4 seeds.

Glossy buckthorn

  • Shrub grows up to 7 metres (23 feet) tall.
  • Leaves are dark green and glossy
  • Outer bark is gray/brown with small white openings.
  • Twigs and stems have no thorns.
  • Flowers are white with five petals.
  • Fruit is light green, ripens to red, then black in late summer, contain 2 to 3 seeds.

Left uncontrolled, common buckthorn (Rhamnus cathartica) and glossy buckthorn (Rhamnus frangula) form dense thickets which suppress native tree and shrub species. Seeds are widely dispersed by birds can remain viable for up to five years and germinate quickly to take over natural areas.

Japanese Knotweed

  • It grows up to three metres high and its stems are round, hollow, reddish-purple, smooth and look a lot like bamboo
  • Leaves are tear drop shape with pointed tips.
  • Flowers are greenish-white.
  • Fruit is small and white with wings that help to disperse seeds to new sites and seeds are brown and shiny.

Japanese knotweed spreads quickly if not controlled, creating dense thickets that suppress native tree and shrub species. Japanese Knotweed root systems, while strong (it has been known to break through asphalt and concrete) are not as dense as those of native plants, and do not hold soil as well. When Japanese Knotweed grows along stream banks, the bank can become unstable and more vulnerable to erosion and flooding. When it establishes along rivers pieces of roots can break off, float downstream and start growing.