The flowers should be cut before drying out. Thistles will resprout readily if cut down, so it’s best to dig the whole plant up by the root. We have a lot of it and Scotch Thistle in our 2 acre field. Cutting. Apply herbicides to kill thistle, especially in spring and fall, before thistles can flower and seed. Perhaps one of the most noxious weeds in the home garden, Canada thistle (Cirsium arvense) has a reputation for being impossible to get rid of.We won’t lie to you, Canada thistle control is difficult and requires a significant amount of effort to be successful, but the effort you put into controlling Canada thistle will pay off when you have a garden that is free from this annoying weed. We have an infestation due to being unable to spray in April. The old rhyme is, 'Cut thistles in May, they'll grow in a day/Cut them in June, that is too soon/Cut them in July, then they will die.' When the main stem is bare I cut it off above the ground with a machete, there's a stob left about 6 inches tall. Canadian Thistle, or any perennial thistles, exhibit a much more extensive root system than their biennial cousins. Preventing seed production is of utmost importance when attempting to manage thistle populations. Tall thistles should not be sprayed with weed killer. Weeds vary in their susceptibility to herbicides. Because of this intricate design, it’s critical to remove new thistle as quickly as possible, though this often requires the aid of a weed killer to do so. Start by cutting the thistles when they reach about 6 inches tall in early June right before the flowering stage. I'm cutting off buds with kitchen scissors, lopping off the big arms of these thistles which are 5 to 6+ feet tall. Don't let thistle get to the stage in which the stems elongate and begin to produce flowers. Spear Thistles they depend on wind dispersal of the seeds with the seeds usually falling to earth in the first The root is edible, and according to one source, it tastes “like burdock root only better.”While burdock stalks are delicious, I really can’t stand burdock root, and I think it tastes like bitter dirt.Thus, I’m not excited about cooking up a thistle root. Another tradition says that if you cut thistles in August when the Moon is in the sign of the heart (Leo), they will not return. You should also cut it again when you see new growth to prevent it from spreading seeds. Repeated cutting of the crown of biennial thistles 1 or 2 inches below the soil surface will eventually reduce the stand by preventing seed production. Little can be done to effectively manage these plants if they are allowed to flower and produce seed before control occurs. Mechanical control: Mowed thistles will produce new branches from basal buds but close cutting or cutting twice per season will usually prevent seed production and reduce the population over time. Too many nearby desirable plants will be killed. One great way to kill thistles … Thistle Root. Mowing is generally less successful on deep-rooted perennial weeds and brush. Or this one: Cut your thistles before St. John (June 24), And you will have two instead of one. cutting can spread into a 20m patch in just two years. If the Moon is also at full or waning (dark of the Moon), all the better. Cut thistles in July, they’ll lay down and die. Thistles in your garden can be sliced off with a hoe; cut them as close to the ground as possible. Small rosettes can be removed by hand by cutting the plant below the soil surface to prevent regrowth. 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