Ragweed (Common)
Ambrosia artemisiifolia
An inconspicuous annual weed that is a leading cause of late-summer hay fever. Its fern-like leaves and small green flower spikes release large amounts of allergenic pollen from August into fall.
Common ragweed — soft, fern-like, deeply divided leaves; a major hay-fever pollen source.
Image source: Ontario weed-identification reference (OMAFRA / Ontario CropIPM)
At a glance
- Key clue
- Fern-like leaves; plain green flower spikes (no petals)
- Best months
- August to September, when the green flower spikes appear and pollen is released
- Often found
- Backyard, Garden bed, Vacant lot, Fence line
- Easiest to remove
- Mid-summer (before flowering)
Why it's prohibited
Ragweed pollen is a major cause of seasonal allergies (hay fever) for many people, triggering sneezing, itchy eyes, and breathing problems in late summer and fall. Keeping it cut and removed reduces the pollen in the air.
Main identification features
- Fern-like, deeply divided green leaves
- Upright green flower spikes at the stem tips (no showy petals)
- Usually 30 cm to 1.5 m tall, bushy and branched
- Releases clouds of fine pollen from late summer into fall
- Grows in disturbed soil, gardens, roadsides, and vacant lots
Similar plants & look-alikes
- Goldenrod — Goldenrod has showy yellow flowers and is often blamed for allergies, but it is NOT the main allergy culprit; ragweed's green flowers are the pollen source.
- Mugwort — Mugwort has similar divided leaves but they are silvery-white underneath and the plant is aromatic.
Month-by-month identification timeline
August to September, when the green flower spikes appear and pollen is released.
May–June (Late spring)
· 5–20 cmSeedlings appear in disturbed soil with soft, fern-like divided leaves.
Fern-like divided seedling leaves.
June–July (Summer)
· 30–80 cmBushy, branched green plants grow quickly.
Branched, bushy plant with fern-like leaves.
August–September (Late summer)
· 0.5–1.5 mUpright green flower spikes form at the tips and release fine pollen.
Green flower spikes shedding allergenic pollen — peak season.
September–October (Fall)
Flower spikes finish and small seeds form before the plant dies with frost.
Seeds form; plant declines with first frost.
Growth-stage photo gallery
Photos of ragweed (common) at different growth stages — note the visual features described under each one to identify it confidently.
Young ragweed plants ranging from 2 to 6 nodes (about 12 leaves).
A plant with soft, fern-like, deeply divided leaves.
Upright green flower spikes like a row of upside-down bowls — these release the allergenic pollen.
The small seed-producing female flowers tucked in the leaf axils.
A labelled identification figure showing ragweed's key features.
Click any photo to enlarge. Image source: Ontario weed-identification reference (OMAFRA / Ontario CropIPM).
How to remove it safely
Safest resident-friendly approach
Ragweed is an easy plant for residents to manage: pull or hoe it out, including the roots, before it flowers in mid-to-late summer. Removing it before the flower spikes shed pollen is the single most effective step to cut down on hay-fever pollen.
Tools & protection
- Gloves (and a dust mask if you have hay fever)
- Hoe or hand trowel
Best time of year
Mid-summer, before the green flower spikes open and release pollen (before mid-August is ideal).
Monitoring
Check disturbed areas through summer and again next year for new seedlings.
Prevent regrowth
Pull new seedlings each year and keep soil covered or planted, since seeds can persist in the soil.
What not to do
- Don't wait until it's flowering to remove it — you'll release pollen by disturbing it
- Don't let it go to seed; that builds up next year's plants
Disposal
Bag flowering or seeding plants for the garbage. Pre-flowering plants can usually go in yard waste per City rules.
Safety cautions
- If you have hay fever, wear a dust mask and remove plants before they flower
- Basic gloves are enough — ragweed is not a skin hazard, but its pollen is an allergen
When to get professional help
Rarely needs a professional; large vacant-lot infestations may need repeated cutting before flowering each year.
Bag and garbage flowering/seeding plants; pre-flowering plants may go in yard waste per City rules. Remove before pollen release.
Sources
Report a prohibited plant
Found this plant growing on a property? Report it to the City through official Toronto 311.
Report through Toronto 311This page is provided for general educational and reference purposes only. Plant identification results are not a legal determination. Always confirm prohibited plant information using official City of Toronto resources. For hazardous species or large infestations, consider seeking professional advice.
Image credits & usage
Plant photographs are reproduced for non-commercial public education and identification reference only. Sources include Ontario weed-identification (OMAFRA / Ontario CropIPM) and invasive-species fact-sheet materials; all image rights remain with their respective owners. If you are a rights holder with a concern, please contact us through the Feedback page. Photos on this page: Ontario weed-identification reference (OMAFRA / Ontario CropIPM). Contact us.