Getting Rid of Canada Thistle


Can anyone give me an idea on how to get rid of Canada thistle? It has invaded every bed of my garden, and this year, I can't plant a veggie garden, I will have to cover the whole garden with black plastic to kill everything in there.


Hardiness Zone: 6a

Samantha from Pittsburgh, PA



As you already know, Canada thistle is a really tough weed to eradicate. Unfortunately it competes well in deep, well-aerated soils-the same soils most flowers and vegetables prefer. The biggest challenge is the roots. They can colonize areas 3 to 6 feet in diameter. One of the best methods to get rid of Canada thistle is repeated pulling and mowing just when the flower buds are about to open. Pulling and mowing will eventually work to weaken the roots. When done over the course of three years, this method is said to kill up to 90% of the weeds. I actually like your black plastic idea. Dig up the soil well first, cover it with a good layer of compost and throw the plastic on things for the rest of this season. You'll substantially raise the fertility of your soil with the compost, which Canada thistle doesn't like. Next year you'll probably be home free. Maybe you can experiment with container gardening and try growing your veggies in containers for this one season. Burning in the late spring (May/June) can also work well, but must should also be done over the course of several years to be effective. Biological controls and herbicides are risky if your beds are earmarked for edibles.


Good Luck!


About The Author: Ellen Brown is an environmental writer and photographer and the owner of Sustainable Media, an environmental media company that specializes in helping businesses and organizations promote eco-friendly products and services. Contact her on the web at

May 9, 20060 found this helpful

Never had Canada Thistle, but if you're planning on killing it off with black plastic, you can build a garden bed on top of that (or newspaper). Put newspaper (wet pads of it) over the ground and build up layers of earth, compost, grass clippings, dead leaves, etc. 18-24" high and plant in that. More on this subject in the book Lasagna Gardening. (I'm a container gardener but thought this was a terrific idea.)

Cantate, zone 8-9

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May 11, 20060 found this helpful

I live in Canada and don`t know what Canada Thistle is. What does it look like? Can you describe it for me? Maybe I`ve seen it and know of it by a different name. Thanks.

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May 23, 20060 found this helpful

I'm finding that the Canada Thistle has found its way through my black plastic. They are also all over the most shaded side of the house. The only way I know to get rid of them is to buy a hand weed puller and just make a day of it on a regular basis. That new "Weed Be Gone", kills it in about three days, too.

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Anonymous Flag
April 24, 20160 found this helpful

You do NOT pull canada thistle!!! Pulling them only splits the root in 2, thus multiplying the seed in the ground! You need to clip the first sight of one to the ground base, dispose of it immediately and keep doing that for many seasons. If you are pulling them out of the ground, you will NEVER get rid of them and battle more with each subsequent year. Let me guess, you pull one and within weeks 2 or 3 others pop up within inches of where you originally pulled the other one? That's because you're actually reproducing it. Do some more research. You'll see it takes several years to get rid of it. And the seeds in the ground can last up to 20 years. So even total ground kill doesn't do a thing.

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