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Ragweed (Ambrosia artemisiifolia) is a weed commonly found in Montréal. This annual plant is present from May to September and dies when frost hits in the fall. Its pollen causes hayfever or allergic rhinitis in one in six people, which represents more than one million victims.  Ragweed starts to spread towards the end of July, however most of the pollen settles within a radius of one kilometre around the plant.

How to identify ragweed

Ragweed is a plant that measures between 10 centimetres and 1.5 metres in height. It can be identified by its jagged leaves that have 3 separate lobes. It's yellow-green flowers are found in clusters at the top of the stem.

Where does ragweed grow?

It grows in poor soil. In an urban environment, it is often found on vacant lots, in parking lots, along the edge of sidewalks, on playgrounds, at snow dumps, on fill, in flower beds and along roads.

What symptoms does ragweed cause?

The allergen in ragweed is its pollen. The symptoms associated with the allergy are:
- Allergic rhinitis: repeated sneezing, nasal congestion, clear and abundant nasal discharge, itchy nose, palate and ears
- Conjunctivitis: red eyes, tearing, itchy eyes, swollen eyelids
- Asthma: coughing, wheezing and shortness of breath
Quality of life can be disrupted from July to September because of sleep problems, fatigue, irritability and trouble focusing.

If you have any medical questions about allergy symptoms, please call Info Santé at 811.

How to control ragweed

The easiest and most accessible way is to systematically uproot ragweed before it produces flowers towards the end of July. It is preferable to not compost the plant because if seeds are present they could germinate.

Other control methods are also used: cutting and mowing are carried out once in late July and once in late August. Planting herbaceous varieties can help to compete with ragweed and produce its abundance. The use of mulch or a membrane can also help to prevent the plant from spreading.

How to prevent it

People who are allergic to it are recommended to limit their exposure to ragweed pollen by avoiding areas where it is abundant, and by avoiding outdoor activities when the air concentration of pollen is very high between the end of July and the end of September.

What is the difference between ragweed and poison ivy?

Ragweed and poison ivy are to undesirable plants because they are both harmful to our health. Although they are two very different plants, they are often confused. They differ in terms of appearance and symptoms they trigger.


Herbe à la puce

Poison Ivy (Toxicodendron radicans)

Herbe à poux  Ragweed  (Artemisia ambrosiifolia)



- Its sap contains poisonous oil (urushiol) that causes painful inflammation of the skin.
- Contamination can happen with direct or indirect contact with the skin, because the oil can also stick to clothing or to pets.

Causes respiratory allergies.
Symptoms Inflammation of the skin, redness and irritation, formation of blisters on the affected areas. It is not dangerous to touch, however inhalation of its pollen can cause allergic retinitis, conjunctivitis and asthma attacks.


- A plant that can be ligneous, bushy, creeping or climbing.
- The leaves have a reddish tint in the spring, are dark green in the summer and yellow, red or orange in the fall.
-One edge of the leaf is smooth and the other side is irregularly jagged, its leaves are composed of 3 leaflets.
- The central petiole (small stem) on the middle leaflet is longer than the other 2.

- A herbaceous plant with very jagged leaves.
- 10 cm to 1.5 m high.
- Has several flowers grouped together in a cob shape at the tip of the plant.
- Its leaves resemble carrot leaves


It grows along the edge of the forest, on vacant properties, along roads and trails, in parks or along waterways.


It grows in poor soil for instance on vacant lots, along roads, in fields.


A perennial, with reproduction through seeds and underground stems called rhizomes.


An annual plant that dies every year and reproduces with seeds.

Caution: call a specialist to eliminate poison ivy. Do not burn the plant or try to pull it out.

Sources :
Ministère de la Santé et des Services sociaux du Québec
Agence de la santé et des services sociaux de Montréal