Common Cocklebur
Xanthium strumarium
Annual; spreads by seeds; height to 4 feet; found across U.S. and most of southern Canada, except Quebec and northern New England; flowers August through October.
Pull or hoe plants beneath soil line. Can be composted if haven't gone to seed. Use dense mulch to smother seedlings. Thrives in wet soil. Poisonous to livestock; often confused with common burdock.
Photo: (cc) Joshua Mayer/Flickr
Canada Thistle
Cirsium arvense
Perennial; spreads by seeds/rhizomes; height to 5 feet; found coast to coast across northern U.S. into Canada; flowers July through October.
Wearing gloves, dig out plants, removing as much root as possible. Cut down new shoots monthly. Mulch with cardboard. Spread corn gluten in early spring to suppress seedlings.
Photo: (cc) Matt Lavin/Flickr
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