Identifying a Prickly, Serrated-Leaf Weed in Ontario: Resources for Weed ID

The Weed Description

Tall, resembles marijuana or mature kochia, but leaves are serrated (not spade-shaped). Extremely prickly, hard to pull by hand. No flowers observed. Increasing each year in Ontario lawn.

Best Identification Resource

Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) maintains an excellent online weed ID guide with photos, life cycles, and control info:

https://www.omafra.gov.on.ca/english/crops/field/weeds/problem_weed.htm

How to Use It

1. Click through each weed link.
2. Compare photos to your weed.
3. Read life cycle (annual/biennial/perennial) to time control.
4. Note preferred conditions (indicates soil issues).

Likely Candidates

• Canada thistle (Cirsium arvense): Prickly, serrated, perennial, spreads by rhizomes.
• Bull thistle (Cirsium vulgare): Biennial, very prickly, rosette then tall stem.
• Prickly lettuce (Lactuca serriola): Annual/biennial, serrated, prickly midrib.
• Sow thistle (Sonchus spp.): Similar to dandelion but prickly.

Organic Management (Once ID'd)

• Perennials (Canada thistle): Persistent digging, sugar/compost to favor grass, prevent seeding.
• Annuals/biennials: Mow before seed set, corn gluten pre-emergent, improve soil.
• All: Healthy dense lawn = best prevention.

Why Local ID Matters

Weed species vary by region. Ontario's climate and soil select for specific weeds. OMAFRA's guide is tailored to your conditions—use it.