While Canada Thistle is a fairly tough cookie control can be acheived without spending lots of money on a glyphosate product. I have never seen any available in quantities small enough, and inexpensive enough, to not kill off everything that grows on my 1.75 acres.
Since birds like the seeds, Goldfinches use the fluff to build nests, if any plants are growing within about a mile of you there will be seeds dropped that can germinate and grow. As already stated this bugger can grow back from any bit of root not removed.

Usually, we pretty much agree, kimmsr, but on this one we'll have to agree to disagree.

Canadian thistle is different, and it both can and will take over everything. You say control can be achieved without this, but you don't say how....

For about $25 (pricey, but the best investment I have made in years), you can get either the diluted form in the pump sprayer, or the concentrate to dilute and use in your own sprayer. It will be enough to deal with a serious infestation in a large yard/garden, and you'll have plenty left over to deal with the few extraneous resprouts. It lasts well in an unheated garage, and will work next year for any new ones that birds plant.

And you are right that birds, particularly goldfinches, love thistles. I have a couple of other native thistles that I actually encourage, and let go to seed. The goldfinches are just as happy with those. But if *they* get in the wrong place, or become a problem, you can dig them out! Not so with the Canadian thistle.

I have spent almost as much this year on lawn/leaf bags to break up and bag the dead thistles (very satisfying!), since I did not want the prickly stuff in my compost. Once they are dead, they pull easily, and only very rarely have anything left to resprout. And I just zap those few.

Maybe some of our difference here is also size of property. With not quite 2 acres, I might be feeling less invaded than I have been. Our yard has 100 ft frontage, and about 225 feet depth, so we do a lot of different areas of 'small space' gardening to get variety. What might be minor to you can devastate us.

Anyways,
I still vote for the roundup against Canadian thistles....

When the Thistle plants are young, way before they even think of producing seeds, they are easily pulled with most of the root system and can then be mulch mowed into the nearby turf, if not composted, where the nutrients they pulled from your soil will be recycled.
Tossing into the trash anything that once grew in your soil, except Poison Ivy, Sumac, Oak, is simply a waste of valuable nutrients.

Thanks for the info. I will try the roundup. So far the thistle is only located in half of my garden.

Peaches

Ah, now I'm getting some of the difference here, kimmsr. You are correct, that if they are in or near an area that can be mowed, and if they are caught young, when they first seed in, then I wouldn't have bothered with chemicals, either.

Unfortunately, on my property, the biggest infestations were in places like the large bed of vinca, hostas and ferns between the large herb garden and the rose arbor. And several other complex areas with plants I wanted to keep. And I didn't know enough about the plant early enough in the process.

I pulled them, and pulled them, and then tried to dig them out seriously.... I had been used to other thistles. No big thing. But it seemed that all I was doing, with all the hard work over several years, was helping them to spread. I would pull a dozen of them, and twice as many regrew. Over and over again. I never let them go to seed. The runners/roots were very clearly winning. I couldn't even manage a holding action....

And I agree, generally, on composting everything. And we do, in many ways, downright creatively [grin]. But by the time the thistles die, there is not much left but the carbon and mineral components. I'm not at all short on those.

And I want to feel comfortable in putting compost around my herbs, and vegetables, and fruits. While glyphosate should not be a problem with that, I would prefer to send it to the city compost facility, where the end result will be used in parks and around street trees.

Glyphosate works on the thistle. With good timing and conditions, one application can do them in. Usually that is not the case. The best time to hit canadian thistle with glyphosate is when it is in the bud stage, or in late summer/early fall a couple weeks before frost. When you hit it at other times of the year, it will burn everything down, but it seems some of the roots will survive to grow again.

In any case, spray it at the right time, then afterwards hit every bit of new growth just after it appears so that you starve the remaining roots by preventing any top growth that can feed the roots.

The best time to control any "weed" is before it produces any seeds, spraying any "weed" with poisons as it is dying in the fall anyway os largely a waste of time, energy, and money.
The only things I have seen about any of the glyphosate products that is good is the ads by the sellers of the stuff, everything else tells me this poison is not something that should be sprayed in the environment. Where it has been used there are signs of genetic mutation in the lower orders of life, fish, frogs, toads, etc. that may show up in humans.

I also have this darn weed and it's a pain in the butt. Like Linda, I started out pulling it and only ended up with more! Since then I have read that all it takes is a piece of root 1" long to produce another plant. Egads! I realized I needed heavy artillery, so I bought some Roundup and sprayed it. I think I sprayed it 3 times now but every time it comes back up, it's less and less. I'm not going to expect it to be gone by next year, but at least I feel like I'm in control of the situation now. Thanks, Linda!!
Cathy

You can beat it, Cathy. I don't know what form you bought, but just fyi, the diluted stuff actually works better than full strength. If you got the concentrate, dilute it per the instructions on the label.

When I first tried it, I tried it 'straight', desperately thinking that tougher was better.... I got some grow-backs and sprouts. I finally got to the less-panicked place where I figured that the chemists might know what they were doing, and diluted it per the label. It worked much better. No regrowth.

It also works better when the plant is actually trying to grow. It may be that in mid-August heat, the plant is less active. May take more time and persistence. But my multiple 'fields' of these things, with their roots, seem to be reliably dead, and have been for several months.

I am starting to plant again, instead of just fighting thistle-wars.

And kimmsr is correct in that this is not a good thing to spray in very large quantities where and when it can easily run off raw into a creek or storm drain. This generally only happens in large commercial applications. In these situations, it can be a problem with aquatic life. But that doesn't ordinarily apply to using it judiciously in your back yard.

Good luck!

The problem with many of these "weed" killers is the synergistic affect that comes from mixing two chemicals. Glyphosates are not terribly bad, by themselves, and the inert ingrediants used, most of them GRAS (Generally Recognized As Safe) products and because of that there is no requirement for the manufacturer to test the safety of the combined product and no one really knows what this product does in the environment.
Back in the 1960's we were told by many chemical companies, "Oh, dumping this waste here will not be a problem." and that is why we have EPA superfund sites still trying to clean these places up. Immediate damage happens where there are large commercial operations but every home that uses these products contributes some, and a few hundred homes can create as much of a problem as one large commercial operation. Keep in mind that the water we have now is all of the water we will ever have, no more is being made and the more we pollute what we have the less we will leave for our grandchildren to have.

I am new to organic gardening and new to understanding that the nasty weed I have been fighting in my garden and lawn is Candian Thistle. Naively, I have been pulling it out for the last couple of years and now I have so much that if one could harvest and sell it, I might be able to pay for my daughters' college costs . . . but that's a separate issue. Lots of good discussion here about eliminating it in the garden, but what about in my turf? Last fall we pushed our garden borders back and laid sod in the bare areas - now I have lots thistle growing up through it. I have read that in the spring it is suggested to cut the thistles off & each time you do that the plant will be weakened as it is expending energy 're-growing' - however, they warn it will take several times of doing this. I have a significant amount of thistle and wondered if you agree on this strategy or if there is any other strategy for dealing with it. I dread how many manhours this may require! Surrounded by C. Thistles in DuPage Cty, Illinois

I believe that if you mow the area regularly, it will not thrive. It is naturally a tall plant and I have never seen it succeed in my lawn nor my neighbor's. The underground roots will spread into garden beds. Do not let your guard down!

My next door neighbor had all of her garden beds infested with canada thistle. I warned her but she did not listen! And she has over an acre of land. She finally had someone use a professional herbicide that specially kills canada thistle but of course it killed all of her other plants too. The lawn did not need to be treated.

I believe that if you mow the area regularly, it will not thrive. It is naturally a tall plant and I have never seen it succeed in my lawn nor my neighbor's. The underground roots will spread into garden beds. Do not let your guard down!

My next door neighbor had all of her garden beds infested with canada thistle. I warned her but she did not listen! And she has over an acre of land. She finally had someone use a professional herbicide that specially kills canada thistle but of course it killed all of her other plants too. The lawn did not need to be treated.

Hello,

I bought my home a year ago, and noticed some thistle last summer, but I have lots more this summer. It's mostly in my flower beds, with a few that have spread into the lawn. After reading a few of these threads, I will stop pulling them and start with the Roundup. Should I apply Round up now, or wait until late summer? Many of them are over 12" tall, though some are under that, but I believe the small ones will get to over 12" within a few weeks. I'm a little embarrassed at how large they are, and am afraid the neighbors would think I am neglecting my yard if I waited until August to spray.

Any thoughts? I am trying to balance short term appearances with a goal toward long term eradication. I'm very new to gardening, so please forgive me.

Then, and I apologize for such a newbie question, but once I spray and the thistle looks dead, what do I do? Do I pull them by hand, rake them up, or does it matter? And do I have to get all of the roots? I assume once they are hit with Round Up that there's no more viable seed or roots, so if some root is left in the ground that isn't a problem? I just don't want to leave anything behind that will come back later! Thanks.

http://www.btny.purdue.edu/Pubs/WS/CanadaThistle/CanadaThistle.html

Here is some info from Purdue. They suggest treatment in early June when the first flower buds appear. Once the thistle looks dead, you can remove it. But it will probably come back some from the roots and you need to keep on it.

Dont be too embarrassed because your neighbors probably have it or had it at some time. It is good that you are trying to take care of the problem because it will only get worse and will never go away on its own.

We never had thistles until the house next door went in foreclourure. It has sat empty for 7 years and never been mowed. The yard is full of thistles. They grow so tall all around the house. I fight them constantly. I dig down as deep as I can to get them out. Then I watch to see if they come back up. If I see a small start I hit them with Roundup!! Seems to be working.. Until this house next door gets sold we will fight them.

Do NOT try to pull this weed out of the ground.

Do NOT try to dig up this weed trying to get all the roots.

The best approach is to keep the tops of these weeds cut off so that they can’t go to seed. But leave enough stalk and foliage that you can saturate it with Round-Up.

Then pray.

We got Canadian thistle under control glyphosate (studies that do not have friends of Monsanto involved or other conflicts of interest show it as 'carcinogenic' or 'probably carcinogenic' - it just wasn't worth the risk to my loved ones and neighbours).

We moved into our house 5 years ago - 100' x 50', so the thistle seemed to take over our little yard. It was a nightmare. They grew in hardpan here, so pulling up WITH their roots is literally impossible without heavy equipment (the roots supposedly can grow up to 20' down). Here's what we tried:

1) On advice from experts we tried cutting them back when they were still young. They kept growing back, and more - probably from the roots getting stronger.

2) On advice from more experts we tried cutting them down just before flowering - the theory being that all their energy goes into flowering and they will eventually die this way. They kept growing back.

Options 1 and 2 were very time-consuming and only a band-aid to the problem, so I tried number 3:

3) I did extensive research and found that the USDA did a study in 2002 and found that 20% vinegar (acetic acid) killed 80-100% of Canada thistle. So we sprayed them - young/small and old/large. I even tracked some that I sprayed to see if they regrew from the same roots, and those did not. For the really large ones (3-ish ft tall), I cut them back to 6" or less, then sprayed. Needed to hit them a few times because their root systems are probably very strong. I even sprayed a 3' tall one through the fence, in the neighbour's yard, and it worked - that one surprised me!

For the first 2 years, we had to spray all summer because there were so many. Now we only need to spray weedlings occasionally - mostly in the hottest part of summer. Most of our neighbours still have a problem with them - they either don't spray with acetic vinegar or only spray after they have a lot of mature thistles.

Canada thistle is now my least problematic weed. Still haven't gotten those dandelions under control, and oh, the horsetail weed!

I know this is an old thread, but hope this helps anyone who finds it in search of help for this tenacious weed.

PNW that is very interesting. Glysophate is now illegal in many canadian cities except for golf courses. 20%vinegar is such a strong acid how did you manage it? Did you need special protective clothing? Did you use a special sprayer ? I wonder if it can be painted on the plants rather than spray.

Blue. First, I meant to write "without Glysophate" - it won't let me edit it now ;)

I've moved up to 30% vinegar now. I have used a hand spray bottle and a 2 gallon pump sprayer. I don't do it on a windy day, and it works best if you wait till it's warm and super sunny. I've even had some success when it's cloudy, but more when the sun can really blast it.

It's now much easier to find in our local hardware and garden stores than it was 2 years ago, when I had to order it online - even though we live in a small town where purchasing items is very limited.

I don't wear special clothing - just gardening gloves, jeans, and short sleeve tops (a long sleeve top will be safer, of course). Make sure your spray bottle does not dribble because regular garden gloves are not waterproof. And goggles are a good idea (though I just wear my regular glasses and have never sprayed my eyes).

I'm sure you could paint it on, if you've got the time and inclination. Best of luck to you!