Asked May 13, 2018, 9:32 AM EDT
Sherburne County Minnesota
Thank you for the question. Controlling thistle, no matter the variety, will require patience and perseverance. A combination of herbicide and hand pulling will offer some control this year. Next year, be on the lookout for young plants and remove them ASAP. You will need to identify the thistle you have in order to best battle it. This publication will help you identify the plant: https://www.ag.ndsu.edu/publications/crops/perennial-and-biennial-thistle-control-w799Read
This publication gives you information on how to control the thistle, once identified: https://www.extension.umn.edu/garden/yard-garden/weeds/thistle-control/
You can hand pull the volunteer trees or use a product like Roundup on them. A plan of action might look like this:
1. Concentrate on weed eradication this summer and fall.
2. This fall, establish the borders of your perennial beds so that in the spring you are ready to plant.
3. Next spring, plant preferred perennials and mulch around them, including the rest of the flower bed surface. This will keep sunlight from reaching the soil and fewer weeds will sprout.
4. Realize that new trees will sprout every year from seed and bits of thistle root and seed will sprout. You will have to continually do a low level of weeding.
To improve the look of the flower beds this summer while you eradicate weeds, you could fill some nice planters of different sizes with beautiful annuals, grasses, even perennials, and arrange them in groups under the trees. A birdbath among the planters would look nice too. These would draw the eye, instead of the weeds.
Good luck and thank you for contacting Extension.