Up to my ears in thistle! - Ask Extension
We moved into a home with overgrown gardens. I’ve done so much work but I just can’t beat the thistle. The thistle I’m most concerned with is m...
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Up to my ears in thistle! #868819
Asked May 16, 2024, 11:27 PM EDT
We moved into a home with overgrown gardens. I’ve done so much work but I just can’t beat the thistle. The thistle I’m most concerned with is mixed with a huge and healthy hydrangea. I don’t want to kill the hydrangea but smothering the thistle with cardboard and 4” of mulch didn’t do much last year. It just spread further out. Help!
Anoka County Minnesota
Expert Response
Thistle cannot be pulled out because when the root breaks it makes two plants. Every piece of root can make a new plant. The roots also go down 12-16 ft. Amazing!
Chemical control is the only way to kill thistle unless it’s possible to get out all the root.
Since the thistle is under a hydrangea dip a paint brush in Roundup or other brush killer and paint the thistle leaves, take great care not to get any on your shrub. It may take several applications. Follow the directions on the label for killing thistle. If you don’t want to use a brush killer. Put down multiple layers of cardboard over the thistle seal all the edges so no light gets to the plant. Don’t cover all the soil around your shrub because it needs water and air for its roots. It will take a couple of years to get rid of it.
Chemical control is the only way to kill thistle unless it’s possible to get out all the root.
Since the thistle is under a hydrangea dip a paint brush in Roundup or other brush killer and paint the thistle leaves, take great care not to get any on your shrub. It may take several applications. Follow the directions on the label for killing thistle. If you don’t want to use a brush killer. Put down multiple layers of cardboard over the thistle seal all the edges so no light gets to the plant. Don’t cover all the soil around your shrub because it needs water and air for its roots. It will take a couple of years to get rid of it.
