How to treat Canada thistles near vegetables - Ask Extension
Hello,
I’m new to the Midwest as well as to gardening. Our backyard has a pretty heavy invasion of Canada thistles. We were told that 2-4 D would h...
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How to treat Canada thistles near vegetables #928866
Asked April 19, 2026, 12:27 PM EDT
Hello,
I’m new to the Midwest as well as to gardening. Our backyard has a pretty heavy invasion of Canada thistles. We were told that 2-4 D would help combat it, which it definitely has, although they are still quite prevalent. Our neighbors have the same issue and tend to let them go to seed, so I fear this will be an ongoing battle. This year I’m planning on growing quite a few vegetables and flowers in grow bags since the ground is still a work in progress. How should I treat the thistles while not damaging my vegetables and flowers? Should I tarp them while spraying? Is there a safer or organic alternative such as cleaning vinegar? Also, how long after treating would the ground be safe for planting?
Thank you so much for volunteering your time and support, I greatly appreciate it
Wright County Minnesota
Expert Response
Hi, Thank you for writing.
Vinegar does not work.
You are on the right track with solarization. For this you put on clear, not black tarp. You want light to encourage germination and lack of water to kill the plants. https://extension.umn.edu/planting-and-growing-guides/solarization-occultation
Considering that your ground has been neglected for a while, I would just leave the clear thin painter's tarp (with rocks to anchor it) all season and plan for a garden next year.
2-4 D is extremely toxic to veg and tends to drift inclulding from your neighbor's lot to yours.
https://extension.umn.edu/planting-and-growing-guides/herbicide-injury-garden-plants Solarization will let you avoid using it.
As for your neighbors, have them over for tea and tell them how you both have an interest in getting rid of thistles. Perhaps you could learn to grow tomatoes together without 2-4 D
Vinegar does not work.
You are on the right track with solarization. For this you put on clear, not black tarp. You want light to encourage germination and lack of water to kill the plants. https://extension.umn.edu/planting-and-growing-guides/solarization-occultation
Considering that your ground has been neglected for a while, I would just leave the clear thin painter's tarp (with rocks to anchor it) all season and plan for a garden next year.
2-4 D is extremely toxic to veg and tends to drift inclulding from your neighbor's lot to yours.
https://extension.umn.edu/planting-and-growing-guides/herbicide-injury-garden-plants Solarization will let you avoid using it.
As for your neighbors, have them over for tea and tell them how you both have an interest in getting rid of thistles. Perhaps you could learn to grow tomatoes together without 2-4 D
