Weeds: October is a great month to treat aggressive perennial weeds such as Canada Thistle and creeping bellflower. Perennial weeds, with their persistent and vigorous roots are very difficult to control through pulling alone. UW-Extension advocates using an IPM (Integrated Pest Management) approach wherein you use cultural methods first to solve problems and only turn to chemical controls (whether organic or traditional chemical controls) as a last resort.

Unfortunately, with these two weeds, chemical control may be needed for large infestations. Since perennial weeds are preparing for dormancy at this time of year, they are pulling photosynthates from their leaves down into the root system to store the energy for next year. This process also aids the absorption and translocation of herbicides, so they are often more effective now than other times of the year. Canada Thistle has an extensive underground root system consisting of horizontal roots that then push up vertical roots and shoots every six inches or so along their length. So even when you get several inches of vertical root as you pull a Canada thistle, you don’t remove the horizontal mother root that continues merrily on its way. You can “starve” the horizontal root with repeated pulling, but it takes persistence and vigilance. You need to check for new rosettes pushing up out of the soil every week and remove them promptly. Since they seem to like to emerge under the leaves of other plants, this can be a challenge! Several years may be needed for good control.

Creeping bellflower has very persistent vertical storage roots that are usually 4 to 6 inches below ground as well as smaller horizontal rhizomes that travel in the soil and pop up rosettes of leaves that grow into new plants every 3 to 6 inches along their length.

This plant is insidious. I’ve been battling it in my garden for 10 years and it is still winning! If you are able to remove both the vertical and horizontal roots from an area, and not leave any pieces behind, it will control the plant. Often, as in my garden, this is a long-term battle. The big problem is when the infestation spreads into other plants, such as perennials that you want to keep.

Creeping bellflower has a pendulous light purple flower on a tall stalk and narrow but heart-shaped leaves. In shady areas, it may not flower, but still produces lots of leaves.

UW-Extension weed specialists have created fact sheets on these two species, which are available for viewing, downloading and printing from the UWEX learning store site https://learningstore.uwex.edu/. On the site, go to the search box on the right hand top side of the screen. Type in “creeping bellflower” or “thistle” to find those particular fact sheets. You don’t have to buy the publication to view it or print it. Scroll down to the box marked ‘View the Publication’ to view and print.

Lisa Johnson, Dane County UW-Extension horticulture educator

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