Toxic weed discovered in Ottawa

A giant, toxic weed whose sap can produce skin boils and even blindness has been found in two locations within city limits, officials with the City of Ottawa say.
Giant hogweed can grow to a height of six metres. (CBC)
A giant, toxic weed whose sap can produce skin boils and even blindness has been found in two locations, say officials with the City of Ottawa. One of the poisonous plants was spotted in a family's backyard, another in a public park.

The city is not releasing the exact locations where the Giant Hogweed plants have been found, but David Barkley, manager of forestry services, said one was found in Ottawa South and the other the west end of the city. He added that the one on the private property has been removed, but that the city was in the process of hiring a private company to remove the one in the city park.

The plant is most easily identified by the purple colour on its stem. (CBC)
The giant hogweed grows up to six metres in height and can produce tens of thousands of seeds. Its sap reacts with human perspiration, producing boils on the skin and even blindness if it comes in contact with the eyes.  

The weed was reported in Renfrew County last week. It's originally from Asia but has been spreading across Canada for decades.

Barkley said city council has been apprised of the problem and will be meeting this week to discuss how to deal with the weed.

Giant Hogweed fact sheet


Giant Hogweed is a serious invasive plant that poses a moderate threat to human health and safety. The plant is native to Europe and Asia and was introduced to Canada as an ornamental. It is found in many areas in southern Ontario, and has recently been discovered in Renfrew County and small populations have been confirmed in the Ottawa. In each case municipal staff has started localized removal of the plant.


Giant Hogweed is a long-lived perennial plant. It can take three to four years before flowering and flowers only once in its life. It can range in height from one to 5.5 metres. Plants produce huge leaves that are up to a metre in width. Leaves are deeply cut, with large lobes and sharp teeth on all leaf margins.

It has sharp pointed bumps on stems and leaf petioles. Stems have reddish purple flecks and are often entirely purple at the base. Stems are mostly hollow and up to 10 cm in diameter. Stems and petioles are densely hairy.

Giant Hogweed flowers from June to August with white (sometimes pinkish) flowers in large clusters.

Distribution and habitat

Primarily found along roadsides, stream banks and disturbed open areas. Plants reproduce well on disturbed sites, and prefer full sun and open habitat common along roadsides and ditches in rural areas.

Ecological impact

Giant Hogweed can shade out and outcompete native vegetation, which is a concern in riparian areas along stream banks and natural areas.

Human health concerns

This plant is poisonous. Its hollow stem, leaves and plant hairs produce a sap if broken that can cause serious skin inflammation on contact. If contaminated skin is exposed to sunlight a more serious reaction can occur including blisters, discolouration and scars. Contact with eyes can lead to temporary loss of vision or blindness.

Giant Hogweed contact with bare skin should be avoided – this includes all portions of the plant. If contact with skin occurs, avoid exposure to sunlight and wash the site immediately. If a skin reaction occurs, seek medical attention.

Those working to control this plant should use goggles and waterproof gloves. Long sleeves, pants and boots should be worn; synthetic materials work best since most fabrics will absorb plant sap or can be penetrated by the plant.

Clothing that comes in contact with plants should be washed. Equipment used to control the plant should be washed with water immediately.

Management and control

Giant hogweed is mainly spread by soil movement and contaminated equipment but can still be found in private gardens. Minimizing soil movement and regular equipment washing can help prevent new introductions.

This plant takes several years to reach its full size and to reproduce. It is easy to see and identify due to its habitat and large size. It should not be removed with a brush saw or weed-eater, but can be destroyed with over-the-counter herbicides.

Suspected findings of Giant Hogweed should be confirmed through the City of Ottawa at 311, or through the Natural Resource Information Centre at 1-800-667-1940, or by visiting