How to rid flower garden of Canada Thistle

Asked September 23, 2017, 10:48 AM EDT

The internet research I've done tells me that my problem is Canada Thistle. It could be another variety but I don't think so. This spring we expanded a flower bed and in preparing the soil we now believe that we have broken up the root system of this blasted thing and spread it all over the flower bed via our tilling of the soil. I feel this is the case as it isn't in any of the other flower beds. What I have read says not to 'pull' them, that due to their root structure it will cause them to produce more. Therefore, I have been cutting them off at the ground level, as my reading directed, but I still am getting more and more! What can I do? I was so looking forward to making this flower bed this summer and stopped due to this problem. Help please!

Jefferson County Kentucky

1 Response

This could be Canadian Thistle but it's difficult to get a positive ID on juvenile plants, especially from a photograph alone. (Identification can be done by bringing an entire plant, as mature as possible, to our office and we will send it to the lab at no cost to you.)

Eradication of Canadian Thistle includes using chemicals. Cutting the plants back help to deplete the energy stored in the roots but is not an effective control, as you have seen. Products that control broad leaf plants (2 4 D) or non selective herbicides like glysophate (such as in Round Up) can be used for effective control. The following publication on Canadian Thistle from the USDA recommends various chemicals and the timing involved to get the best results.
Remember to read and follow all label instructions before applying pesticides.

Feel free to contact our office if you have other questions.

Let me know if I can help you further!

Carol Wilder
Horticulture Technician
Jefferson County Cooperative Extension Service

200 Juneau Drive
Louisville KY 40243