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Health and Environment

Poison Ivy and Other Harmful Plants

Ragweed plant

The municipal by-laws prohibit property owners to allow plants such as ragweed and poison ivy to grow on their land, as they can be harmful to human health or the environment. It is important to learn to identify and eliminate them to avoid problems and stop the spread of these plants. Controlling harmful plants is everyone’s responsibility and requires the cooperation of the entire population.


Sneezing? Teary eyes? The culprit is often ragweed. A very widespread weed in Québec and one of the most problematic plants in the urban environment, ragweed (Ambrosia artemisiifolia) grows from May to October and dies with the first frost in fall. In mid-June, the weed begins to flower and produce pollen. This pollen travels in the air in the form of fine dust, and from July to October, it causes allergic reactions in people who are sensitive to it, which is the case for over 1 million Québecers.

    • Height ranging from 5 cm to 1.5 m with shallow roots
    • Leaves: Very jagged and serrated, deep green on top and a little paler underneath
    • Stalk: Firm, hairy and greyish green, turning red when it flowers
    • At the end of the plant, spiked, yellowish-green flowersté de la plante, fleurs en épis d'un vert jaunâtre

    Ragweed presents no danger on contact with the skin.

  • Ragweed grows in poor soil, but does poorly in thick, fertile lawns. It is found:

    • On the edge of streets and sidewalks
    • On the edges of bicycle paths and railroads
    • On median strips
    • In vacant lots and construction lots
    • On lots that serve as snow dumps
  • The simplest way is still to pull it out. This should be done in June or July at the latest, that is, before it flowers. The proliferation of this weed can be reduced by:

    • Uprooting it before its pollination period (end of July)
    • Raising awareness among your acquaintances
    • Covering the soil with materials such as mulch or wood chips
    • Planting a ground cover that competes with ragweed, such as clover or grass
    • Regularly maintaining your lawn, particularly around the edge of the lot
    • Improving the quality of the soil with compost or fertilizer
    • Using pest-resistant seeds in the bare corners of your property

    If it has not gone to seed, ragweed can be thrown into the compost bin. Otherwise, it must be thrown in the garbage.

    • Public awareness actions.
    • Mowing lots that belong to the city at least twice a year.

Poison ivy

Poison ivy (Toxicodendron radicans or Rhus radicans) contains a poisonous sap that can provoke redness, swelling, blisters and intense itching on contact with the skin, even in winter. These symptoms last for 7 to 15 days after their appearance.

    • It grows in three forms: Bushes, creepers and climbers.
    • Height: 20 cm to 1 m, depending on the form.
    • Three oval leaves from 8 to 55 cm. Leaves are shiny and reddish in April and May, green in June and July, and yellow, orange, red or brown in fall.
    • Clusters of round, pea-sized berries, green to white fruits and whitish to greenish flowers in June and July.
    • Forms large colonies
    • In sun or shade
    • At the edge of wooded areas
    • In vacant lots
    • Along highways and railroads
    • On the banks of waterways
  • Always wear sturdy vinyl gloves and clothing that prevents any skin contact with the plant’s sap. It is important to be well protected during these operations and to properly clean your clothing and tools afterward.

    • Pull up the plant, dig out the roots and remove them.
    • Work the soil frequently to reduce regrowth. Collect the plants or parts of dead plants on the ground in case there are still seeds attached to the stalks.
    • As a last resort, use a low-impact pesticide with sodium chloride as the active ingredient.
    • Throw the plant in the garbage and do not compost or burn any of its parts. Inhaling the fumes from the combustion of the plant may cause serious respiratory problems.
    • Wash all exposed areas as quickly as possible – including under the fingernails – in soap and cold water. Pets should also be washed. An allergic reaction is possible even if you wash your skin, but it will be less severe.
  • The city keeps a registry of the poison ivy throughout its territory to prioritize and plan control interventions in high-risk areas.

Giant hogweed

Giant hogweed first appeared in Québec in 1990. It has been observed in many regions, including Châteauguay. Giant hogweed is an exotic plant that, in addition to disrupting the balance in the ecosystems it invades, presents a danger to human health. The sap contains toxins that, when activated by light, make the skin extremely sensitive to the sun, causing pain and burn-like lesions that can like second-degree burns in extreme cases. This inflammation is characterized by:

  • Redness and swelling of the skin
  • Blisters and pustules
  • Superficial or more severe burns (first or second degree)
    • Giant plant from 2 to 6 m tall that generally form large, dense colonies that spread rapidly and sometimes cover large areas
    • Leaves divided into 1 to 3 leaflets, deeply serrated and pointy, 1.5 m wide and 3 m long with a smooth or slightly scaly underside
    • White flowers growing on a single stem, forming clusters of rounded flowers called umbels 25 to 50 cm in diameter
    • Very sturdy stock from 4 to 10 cm in diameter covered in rough white hairs and reddish-purple blotches
    • In cool, damp environments
    • On vacant lots
    • In meadows and fields
    • Along waterways and in ditches, along banks and shores
    • Along highways, trails and railroads
  • Always wear sturdy vinyl gloves and clothing that prevents any skin contact with the plant’s sap. It is important to be well protected during these operations and to properly clean your clothing and tools afterward.

    • Cut the plant at about 15 cm from the ground.
    • Cut the root to a depth of about 20 cm under the surface with a well-sharpened round shovel.
    • Work the soil to a depth of about 24 cm. This will reduce regrowth.
    • Begin in early spring and repeat every year for several years to totally eliminate the plants.
    • Cover the area with geotextile fabric after eliminating the plants when the colony is not too large and the land does not present too many constraints, to reduce regrowth.
    • The use of herbicides or chemical controls should only be considered as a last resort.
    • Throw the plant in the garbage and do not compost any of its parts.
  • If your skin comes into contact with the sap:

    • Remove the sap as quickly as possible with absorbent paper, without rubbing. Avoid spreading the sap on the skin.
    • Rinse the surface of the skin thoroughly with water and soap and wash your hands.
    • Remove your clothing and wash them to avoid contaminating other parts of your body or objects.
    • Avoid exposing the affected areas of your skin to natural or artificial light. Wear gloves, pants and a long-sleeve shirt for at least 48 hours. If you have burns, protect the affected area for a week.
    • Use sunscreen with a sun protection factor (SPF) of at least 30 for six months.

    If your skin comes into contact with the sap:

    • First-degree burns are superficial and generally do not require specific treatment. If you have pain:
      • Take a cool bath.
      • Make compresses and soak them in water. Apply the compresses to your burns for 20 minutes, four to six times a day.
    • If you have second-degree burns with blisters and pustules, call Info-Santé 811 for more information on how to treat burns. You can also see your doctor, who can prescribe the appropriate treatment.
  • The city keeps a registry of the giant hogweed throughout its territory to prioritize and plan control interventions in high-risk areas.


Buckthorn was brought over from Europe for ornamental reasons. Considered a pretty, decorative shrub, it is nevertheless very invasive and detrimental to biodiversity and the regeneration of certain wooded areas in southern Québec.

    • Small shrub that grows to nearly 6 m high
    • Production of small black berries
    • It grows very quickly.
    • It adapts to a wide variety of environments.
    • It produces a lot of berries.
    • Its seeds can survive for up to three years in the soil.
    • Its germination rate is very high (over 90%).
    • The stumps can often generate several plants.
  • Buckthorn is taking more and more space at the Centre écologique Fernand-Seguin and harming biodiversity and indigenous species, including two species of hawthorn that are the emblematic plants of the centre. In collaboration with Héritage Saint-Bernard, a not-for-profit environmental organization that protects and promote natural environments, and Nature-Action Québec, the city helped uproot buckthorn at the Centre écologique in 2019 by subsidizing the initiative to preserve the integrity of this eco-territory which serves as a guardian in the conservation of natural habitats, flora and fauna.

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