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Getting Rid of Canadian Thistle

This invasive weed is common in North America and very difficult to get rid of. This is a guide about getting rid of Canadian thistle.


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June 15, 2006


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!


Comment Was this helpful? 1
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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January 3, 2008

To get rid of Canadian thistle, cut them at ground level and pour salt on them. They do come back. I tried it myself because I had lots of salt

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January 22, 20080 found this helpful

When you use any kind of salt on the Canadian thistle

they do not come back.

You need to cut them off at ground level and pour salt on them works best if you can put the salt into the stem,like using a funnel,I used a box of salt that has the mental opening pouring one.Time consuming if you have lots but well worth it:)

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0 found this helpful
May 27, 2005

Does anyone know how to get rid of thistle once and for all?



Answer Was this helpful? Yes
May 27, 20050 found this helpful
Best Answer

Only one thing, ROUNDUP. It does not affect the soil. It will kill anything it touches, so be careful, but it will kill root and all, after 3-4 days, you can till the thistle under or easily pull it out root and all.

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May 28, 20050 found this helpful
Best Answer

We found using Weed Be Gone works. You spray it at the base of the thistle bush and wait how ever long it say's to on the bottle and after the time is up you pull the hole thing out root's and all. You will have to keep doing this until all of them are gone but it sure does help we still have them but not quiet as many any more. I sure hope this will help.

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June 27, 20080 found this helpful
Best Answer

We have 160 acres and had several acres of Canadian thistle to get rid of. I couldn't waste time spraying anything that did not work well and kill the roots. I have sprayed with Curtail by Dow for about three years. It is an excellent product and it kills the tops and roots. I have several areas that were thick with thistle that are totally free of it now. Now I have to search for plants to spray and they may be from seeds that have laid dormant or just blew in. It does not kill grass like Roundup.

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August 25, 20080 found this helpful
Best Answer

If you want a method that does not include the use of harsh chemicals, there is another way. No chemical really ever gets rid of Canadian thistle, anyways. Thistle thrives in less nutrient-rich subsoil, which will be increased by the use of chemicals which keep nutrients out of the soil. Thistle actually doesn't like topsoil! If there are enough other plants and compost contributing to the health of the soil you shouldn't really have a problem with thistle.

It is a pioneer plant which decomposes to create better soil for other plants, and using this information will help you get rid of it. So finally to the method. Cut the thistle down to 6 inches above the soil, BEFORE IT GOES TO SEED, and use the clippings as mulch, then add manure, or compost if you don't have access to manure. Finally add seaweed if you have access to it, because it speeds the process. The thistle will thin out and be gone by the 3rd year. I personally don't consider it to be enough of a problem to use round-up and as long as you keep you soil rich it won't come back.

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June 7, 20050 found this helpful

Th best time to spray thistle (use Roundup) is in the late summer to fall BEFORE the flower goes to seed. If you do it when they begin to flower, they are at their most productive time and therefore when the poison hits, it can really hurt the plant. This was advice from our county weed crew.


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May 18, 20060 found this helpful


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0 found this helpful
June 27, 2006

Recently we stopped raising horses on our farm. I talked my husband into letting one field go wild to attract wildlife and give them a safe haven. We added a brush pile, have dead trees, a stony area and a fence row. We now have fox, deer, rabbits, chipmunks, owl, squirrel and many species of butterflies and birds. However, it is being overrun with Canadian thistle. It seems every year it is so much worse. I hate to use pesticide as I don't want it around. Any good suggestions on how to get rid of most of the thistle. It is ruining our paradise.


NellieMary from West Virginia

Answer Was this helpful? Yes
June 28, 20060 found this helpful
Best Answer

Only sure fire way of getting rid of them is grubbing them. I agree you can top them while the thistles haven't opened as the seeds are immature and won't grow. The insect control will not eradicate, just keep the population down. The insects can't survive if they have no thistles to live on. Roundup will kill them, but if you want no chemicals, grubbing will cure the problem. The seeds can survive for years and in drought years where there is cracking or bare ground they can come back. It's an ongoing battle. There are also many types of thistle the worst being the Californian as develops a huge underground root system this needs spraying to control. The tap root type ones are easily grubbed out. I am not sure about the Canadian, we have scotch and nodding thistles a tap root type here in nz.

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June 28, 20060 found this helpful
Best Answer

Cut the thistle off at the ground level and immediately pour salt on the wet stub. If any are blooming cut the blooms off into a paper bag and burn the bag or you will have a million more next year.

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June 28, 20060 found this helpful

There is supposed to be an insect you can buy that will make the thistle plants infertile, and I haven't tried that. I don't know anyone who has eradicated thistle without chemicals, but I use very very little. First I make sure that none of them go to seed. If you just chop or mow them while they have any purple showing in the buds, they will usually go ahead and mature and make seed. I try to chop them before they get that far, but those I miss, I pick off the purple flowers (get some good rose or welding gloves), bag those up, then chop the plant within a few inches of the ground and spot spray my chemical mix right on the open wound. I use WD40 with dishsoap and water. You have to be vigilant. Let one flower head go to seed and you've got a whole new crop next year! 20 years ago, we had huge patches of thistles threatening to take over our farm, now they are few and far between. I can top and spray all of them on our 86 acres in just a few hours.

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June 28, 20060 found this helpful

We have canadian thistle too. I use roundup, but not save for animals.

Try this homemade recipe I found.

Like roundup it must be sprayed on a sunny day to allow the weed killer to work its way into the roots. Good Luck!

Natural Weed Killer Formula

1 gallon White Vinegar

1 cup Table Salt

1 tablespoon Dish Detergent

Remove about 2 cups of Vinegar from the container, pour in salt and dish liquid, shake well to mix, pour the 2 cups of vinegar back into the container and shake lightly. Fill a spray bottle and use as needed. Spray in full sun. CAUTION: It kills all the plants or weeds it touches, but is harmless to animals

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July 27, 20160 found this helpful

If the drainage eventually goes to a stèam, will it affect the fish?

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