How to Identify and Treat Common Lawn Weeds in Ontario (With Photos)

Every Ontario homeowner knows the frustration — you've mowed, watered, and fertilized, yet weeds keep showing up. The truth is, weeds are a symptom of underlying lawn health issues. A thick, healthy lawn is the best weed prevention. But when weeds do appear, knowing exactly what you're dealing with is the first step to eliminating them.

1. Dandelions (Taraxacum officinale)

The most recognizable weed in Ontario lawns. Dandelions are broadleaf perennials with deep taproots that can reach 25 cm into the soil. They spread by wind-blown seeds and are most active in spring and fall. In Ontario, the cosmetic pesticide ban means you can't use traditional herbicides — but there are effective alternatives.

• Manual removal: Use a dandelion weeder tool to pull the entire taproot — if you leave even 2 cm of root, it will regrow
• Iron-based herbicides (Fiesta/Weed-B-Gon): These are legal in Ontario and effective on dandelions. Apply when temperatures are above 15°C
• Corn gluten meal: Apply in early spring as a pre-emergent to prevent dandelion seeds from germinating
• Prevention: Overseed bare spots immediately — thick grass crowds out dandelions

2. Crabgrass (Digitaria)

Crabgrass is an annual grassy weed that thrives in hot, dry conditions — making it a major problem in Ontario summers. It germinates when soil temperatures reach 13-15°C (typically late May in the GTA) and dies with the first frost, but not before dropping thousands of seeds.

• Prevention is key: Apply corn gluten meal in early spring (mid-April) before crabgrass germinates
• Mow high: Keep your lawn at 3 to 3.5 inches — taller grass shades the soil and prevents crabgrass seeds from germinating
• Water deeply but infrequently: Crabgrass loves shallow, frequent watering. Water 1 inch per week in 1-2 sessions
• Overseed in fall: Thick turf is the best defense against crabgrass the following spring

3. White Clover (Trifolium repens)

White clover used to be included in lawn seed mixes and is making a comeback as a 'micro-clover lawn' trend. However, if you prefer a pure grass lawn, clover can be persistent. It thrives in lawns that are low in nitrogen — which tells you the solution: fertilize properly.

• Fertilize with nitrogen: Clover fixes its own nitrogen, so it out-competes grass in low-nitrogen soils. Regular fertilization tips the balance back to grass
• Iron-based herbicides: Products like Weed-B-Gon are effective on clover and legal in Ontario
• Hand pulling: Effective for small patches, but clover spreads by stolons so you need to get the runners too

4. Creeping Charlie (Glechoma hederacea)

Also called ground ivy, Creeping Charlie is one of the most difficult weeds to control in Ontario. It spreads aggressively by stolons and thrives in shady, moist areas. Its round, scalloped leaves and purple flowers in spring make it easy to identify.

• Improve drainage: Creeping Charlie loves moisture — fix any low spots or drainage issues
• Increase sunlight: Trim tree branches to reduce shade where possible
• Borax solution: A carefully measured borax-water solution can suppress Creeping Charlie (use 280g borax per 10 litres of water per 100 m²)
• Manual removal: Rake up stolons before mowing to prevent spreading, then pull by hand

5. Plantain (Plantago major)

Broadleaf plantain is common in compacted Ontario soils. Its presence is a sign your soil needs aeration. It has large, oval leaves with prominent parallel veins and produces tall, narrow seed stalks.

• Core aerate your lawn: Plantain thrives in compacted soil — aeration fixes the root cause
• Hand pull: Easy to remove with a weeder tool as they have a shallow root system
• Overseed after removal: Fill the gaps immediately to prevent re-establishment

The Ontario Cosmetic Pesticide Ban — What You Can Use

Since 2009, Ontario has banned most cosmetic pesticides for lawn care. However, several effective products remain legal:

• Iron-based herbicides (Fiesta, Scotts EcoSense Weed-B-Gon) — effective on broadleaf weeds
• Corn gluten meal — natural pre-emergent that prevents weed seeds from germinating
• Horticultural vinegar (20% acetic acid) — non-selective, kills any plant it touches
• Manual removal tools — always legal and very effective with persistence