First, quick reality check: not everyone agrees that “weeds are weeds.” Some plants we call weeds are genuinely beneficial (pollinators love them, soil loves them), some are invasive in Ontario and should be taken seriously, and some simply have a bad rap because they show up where we don’t want them.
So instead of “kill everything,” this guide helps you decide what you’re dealing with, and what level of action makes sense.
Below are common weeds in Eastern Ontario, where they show up, how to manage them, and whether they’re beneficial, invasive, or neither.
Chickweed
Weed status: Beneficial / “bad rap” (edible; early-season ground cover, but spreads fast)
What it is: Cool-season annual with small white flowers.
Where it shows up: Thinning lawns, after topdressing, and in moist soil with good sun exposure.
How to manage it: Hand weed first, then spot treat with weed control spray if needed. Long-term, overseed to thicken turf and crowd it out.
Lambs Quarter
Weed status: Beneficial / “bad rap” (edible; nutrient-rich, but can take over beds)
What it is: Annual weed that can reach 1.5 m tall and spread to ~40 cm wide.
Where it shows up: Bare loose soil or tilled soil (veg plots and gardens).
How to manage it: Hand weed early, mow if in lawn, and spot treat with weed control spray where appropriate. Mulch helps reduce re-seeding.
Purslane
Weed status: Beneficial / “bad rap” (edible groundcover, but spreads aggressively)
What it is: Annual succulent with red stems and clustered leaves.
Where it shows up: Often after rototilling/cultivating; can appear anywhere.
How to manage it: Hand weed (get roots), then mulch to prevent re-growth and new seedlings.
Canadian Thistle (and Bull Thistle)
Weed status: Invasive (Ontario)
What it is: Perennial that can grow to 1.2 m tall and 60 cm wide; bull thistle is similar.
Where it shows up: Wide range of soils and moisture conditions.
How to manage it: Hand weed carefully (spines), then treat with weed control spray. Persistence matters, thistle roots can keep returning.
Dandelion
Weed status: Beneficial / “bad rap” (great early pollinator food; not invasive)
What it is: Very common perennial with yellow flower head.
Where it shows up: Lawns, gardens, ditches, fields.
How to manage it: Hand weed (remove as much root as possible), spot treat if needed, then overseed to crowd out next season.
Clover
Weed status: Beneficial (pollinators + nitrogen-fixing; not invasive)
What it is: Perennial ground cover crop (some still treat it as a weed).
Where it shows up: Most soils; often where lawns are thin.
How to manage it: Hand weed if you want a pure turf lawn; spot treat with weed control spray if eliminating. If you don’t mind clover, it can actually help fill thin areas.
Creeping Charlie (Ground Ivy)
Weed status: Invasive / aggressive (commonly treated as invasive in Ontario gardens)
What it is: Perennial evergreen creeper; very difficult to control.
Where it shows up: Shady, moist areas; spreads quickly via runners and seed.
How to manage it: Strengthen turf with overseeding in spring and fall, reduce shade/moisture where possible, and stay consistent, this one takes time.
Crabgrass
Weed status: Neither (but a nuisance) (not invasive, just a very common annual lawn invader)
What it is: Annual grass; reseeds and dies back with frost.
Where it shows up: Lawns, driveway/road edges, hot compacted areas.
How to manage it: Hand weed early, spot treat, then overseed. For prevention, apply Corn Gluten Meal in spring and fall.
Poison Parsnip ⚠️
Weed status: Invasive (Ontario) + hazardous
What it is: Perennial/biennial-type weed with yellow flowers in the second year.
Caution: Sap can cause serious burns to skin and eyes.
Where it shows up: Lawns and fields.
How to manage it: Do not casually handle. Call a professional or contact 311 (City services) for safe removal.
A simple way to decide what to do
When you spot a “weed,” ask:
-
Is it invasive or hazardous?
→ Remove/contain ASAP (ex: Canadian thistle, poison parsnip, creeping charlie). -
Is it beneficial (and you don’t mind it)?
→ You may choose to keep it (ex: clover, dandelions, chickweed in small amounts). -
Is it just showing up because turf/soil is weak?
→ The fix is often thicker lawn + better soil, not just spraying.
The long-term secret: thick turf crowds out weeds
Most lawn weeds are a symptom of:
- thin grass
- compacted soil
- shade + moisture imbalance
- mowing too short
- inconsistent watering
If you want fewer weeds next season, focus on:
- overseeding
- mowing higher (especially in summer)
- deep watering (less often)
- aeration for compaction
Need help identifying what’s in your yard?
Bring a photo (or a sealed sample) and we’ll help you identify the weed, confirm whether it’s beneficial, invasive, or neither, and choose the best next step for your lawn or garden.
