How to get rid of Canada Thistle - Ask Extension
I have a landscape bed on the back of my home and it is covered with what appears to be Canada thistle. A neighbor killed it once with a product con...
Knowledgebase
How to get rid of Canada Thistle #927940
Asked April 09, 2026, 4:00 PM EDT
I have a landscape bed on the back of my home and it is covered with what appears to be Canada thistle. A neighbor killed it once with a product containing Clopyralid, but it is back again this spring. The back of my home in Maineville, Ohio in Warren County faces northeast and is shaded from the sun after noon. I found a product called Thistledown on Amazon that has this ingredient listed. Is it safe to use or is there a better solution. I had no luck with commercial products from my local hardware stores.
Warren County Ohio
Expert Response
Thank you for your question to Ask a Master Gardener Volunteer with eXtension.
Your picture does show a healthy stand of Canadian Thistle.
First off, what your neighbor did last fall (using an herbicide containing Clopyralid) was the first round at attacking this persistent perennial plant that spreads by seeds and underground roots. It is difficult to eradicate and can take up to several rounds of consistent treatment to be successful.
I am attaching the following websites for your information. They will give your further information on the timed application and products to use to help you eliminate the thistle.
https://www.btny.purdue.edu/Pubs/WS/CanadaThistle/CanadaThistle.html
https://www.nwcb.wa.gov/images/weeds/Canada-thistle_Franklin.pdf
https://yardandgarden.extension.iastate.edu/how-to/control-canada-thistle
The above mentioned sites list several selective herbicides to assist in the elimination of your Canadian thistle including Clopyralid. Please see the below site to confirm the safety of use of this chemical. As with all products - the label is the law and directions should be followed precisely.
https://ipm.ucanr.edu/home-and-landscape/pesticide-active-ingredients-database/active-ingredient-details/?uaiKey=119#gsc.tab=0
Remember several applications may be needed to be rid of this stubborn plant. Be diligent!
Best of luck to you.
Your picture does show a healthy stand of Canadian Thistle.
First off, what your neighbor did last fall (using an herbicide containing Clopyralid) was the first round at attacking this persistent perennial plant that spreads by seeds and underground roots. It is difficult to eradicate and can take up to several rounds of consistent treatment to be successful.
I am attaching the following websites for your information. They will give your further information on the timed application and products to use to help you eliminate the thistle.
https://www.btny.purdue.edu/Pubs/WS/CanadaThistle/CanadaThistle.html
https://www.nwcb.wa.gov/images/weeds/Canada-thistle_Franklin.pdf
https://yardandgarden.extension.iastate.edu/how-to/control-canada-thistle
The above mentioned sites list several selective herbicides to assist in the elimination of your Canadian thistle including Clopyralid. Please see the below site to confirm the safety of use of this chemical. As with all products - the label is the law and directions should be followed precisely.
https://ipm.ucanr.edu/home-and-landscape/pesticide-active-ingredients-database/active-ingredient-details/?uaiKey=119#gsc.tab=0
Remember several applications may be needed to be rid of this stubborn plant. Be diligent!
Best of luck to you.
