Canada thistle is one of the most ferocious weeds in the entire garden, and this is how we controlled it. Let’s go!
Now, Canada thistle might not be your invasive weed; it was just ours. You might be suffering from something like tiger grass, fire grass, bindweed, knotweed, or a whole host of other very invasive weeds that exist. And hopefully, by the end of this article, you’re going to be courageous to take it on head-on and not feel like you have to move your entire garden or burn everything down with fire. It is possible, and you can get it under control pretty simply.
So, the first method that we tried with no avail was cardboard sheet mulching. Now, I’m a huge advocate of cardboard sheet mulching because it could be simpler. Simply take some plain cardboard and throw it down. You can do one, two, three layers, stick however much you want. And the great thing is, when you throw this down, what’s going to happen is it’s going to smother the weeds underneath from sunlight. They need sunlight to photosynthesize and create energy, and without it, they start to wither.
Now, there’s one downside to Canada thistle, at least, and that’s that Canada thistle is a communal weed. And that basically means that it will travel via the root system. If you leave a root fragment or it is allowed to create new roots, those roots will then shoot off about a foot to two feet in any other direction and then grow up again. And that can be very discouraging because all you need is a little bit of a gap or, in some cases, not enough cardboard to where it can grow underneath. The plant actually grows up and begins to travel. And as long as it can go to where it can reach sunlight, it’ll continue to travel. Believe it or not, I’ve seen Canada thistle come up in a bush, in a boxwood that was 2 and 1/2 to 3 feet off the ground. And this thing just got leggier than a pole bean, just got super leggy. And then once it reached the sunlight, it was game over; it was thriving in between a boxwood. These things are the most resilient, aggressive weeds that I’ve ever come across. But I know some of you down south, you guys have some pretty vicious ones as well. But I found out real quickly that we did this whole garden with cardboard sheet mulching, and within 2-3 months, they were right back to where they were, maybe even a little bit stronger.
The second method that we tried with no avail was a vinegar spray. Now, vinegar is a really strong acid, and it can be an amazing weed killer if it’s used at the right time of year, at the right stage of the plant’s growth. It can be very effective against certain weeds, but not Canada thistle, because Canada thistle, again, is a communal weed, meaning you kill one, and there’s another one popping right up a foot away. So we’d go through and spray the foliage down with a vinegar solution during a nice hot, sunny day like this. And over the course of a week, that foliage would turn brown, it would start to wither, and eventually, it would die. But what would happen is maybe not even a week or two later, you’d see another little shoot pop up. And that’s because we weren’t killing the root. The roots store the energy that the plant is creating from the sun. So the plant is just the tip of the iceberg; the real problem is underneath the soil. So vinegar was out.
So, what did I turn to? Well, I turned to one of the only other organic methods that I knew about at the time, and that was cornmeal gluten. Now, cornmeal gluten is an organic option and is actually really affordable and very effective.
You go to your local grocery store, you pick up a bag of it, super affordable, very inexpensive. And it essentially has an enzyme that inhibits root development of your broadleaf weeds. And so I spread the cornmeal gluten on the plants, and nothing happened. Here’s why: the problem with cornmeal gluten is it falls into a category of herbicide known as a pre-emergent. Now, there are pre-emergent and post-emergent herbicides. You’ve probably seen them. One could be seen with like crabgrass killer, right? Crabgrass killer is a pre-emergent; you use it in early spring, and essentially, it’s an enzyme that acts exactly the same way as cornmeal gluten does, where it stops the root development of a plant emerging from a seed. So you want to apply it before the seeds germinate. A post-emergent herbicide would be something like vinegar that is post-emergent after it already has emerged from the seed and is growing. That’s going to kill the plant. The problem is it doesn’t control the root development after the plant has already sprouted. And so because cornmeal gluten, unbeknownst to me, was a pre-emergent, it did nothing other than help. You know, the Canada thistle basically laughed at me, and I essentially wasted a bunch of time and money. So that was not effective for that reason.
After two long years of battling this weed, that finally led us to our fourth and final way that eventually helped us to control these tenacious weeds. And that’s physical removal. Now, I know this probably seems like the most obvious answer, but the problem is that a lot of gardeners, when they turn to physical removal, they do not actually stick with it. Doing it one time will basically sever the roots like I have here, and all of the other roots that are remaining in the soil are going to continue to sprout. The energy that this plant has created through photosynthesis is now in the roots, and you might take this plant, throw it in the trash, do not compost it, please do not compost tenacious weed, they will continue to come back and proliferate. But those roots are still remaining in the soil. And then what happens is about a foot away, you get another one, and this pops up after a rain, and you let it grow for a little bit, and you might not notice it until it’s grown, and then the roots have grown into the soil and spread to another weed. And so you go through and you remove all those, and you think, ‘Well, I’m quite the clever gardener. I have solved the problem.’ Well, that’s where a lot of gardeners end up running into problems because now what you’ve done is you’ve taken three plants, you’ve severed them off, and then they will fork and they will create six or nine plants. And this might seem like a big problem, but that’s where continuous physical removal will eventually give you the upper hand. And that’s because as these plants start to produce, they can only divide so many times and they can only be cut back so many times during the growing season before the root system starts to lose
that precious energy that it creates through photosynthesis. And so after the course of a full season, we’re talking a full season of every single day coming out and walking in the garden, looking for any tiny little bit of growth, identifying it, and cutting it off, not mulching it, not giving it water, not giving it vinegar, not giving it cornmeal gluten, not covering it up with cardboard sheet mulching, hoping that it would go away, only to have it resurge somewhere else, we’re talking physical removal and being so meticulous about it that we basically had to come out here with a magnifying glass. And ultimately, that is what has led us to being about 98 to 99% free and clear of Canada thistle in our garden. And I am so glad that it’s gone.
So, we do still have Canada thistle in the garden, but as I said, it’s in a much more manageable level, and this has ultimately allowed me to enjoy so much more of my garden. Now, Canada thistle is just, like I said, one small example, and if I’ve learned anything, it’s that this tiny little weed can become an absolutely huge problem if you turn a blind eye to it or just hope that the problem will go away. It will not. It’ll take advantage of you, and it will absolutely make your life as a gardener a nightmare. So, stay up on it, be persistent, and the final thing are some ways to not even get it in the first place. I’m going to talk about three ways that we got it in the garden, or three very potential ways that we got it in the garden, and what we’re going to do about it in the future so we don’t have it happening again.
The first probable way we got it into our garden is through bird seed. Now, we love our neighbors so much, and they love birds, and that’s okay. It’s just one of the risks you take when having bird seed near your garden. A lot of times, bird seed does contain weed seeds, and one of those weed seeds that’s commonly in bird seed are thistle seeds. So just keep that in mind if you have birds around or you feed the birds, you may be inviting an unwanted, very prolonged guest into your garden.
The second probable cause and the one that I think is the most probable: tainted mulch. Now, if you go with free wood chip mulch, a lot of companies don’t screen their stuff. They don’t make sure that it’s free of things like weeds. And if they grind up a stump as well as mulch up your tree or whatever they’re taking care of, all it takes is that teeny tiny little bit of root fragment to then get in your garden and start to spread. Like I said, it only takes a tiny little bit of root fragment, and then you got one plant, and that one plant can turn into two or even three.
And the third and final way you can get invasive weeds in your garden is through tainted compost. Now, compost is made from breaking down organic material and decomposing it to create food and soil for your garden. The problem is if the source of that compost comes from things like yard waste or broken-down weeds, you can very easily get things like weed seeds or even root fragments in your compost. Now, if the compost is heated up and the whole compost is very actively turned, it gets nice and hot. Generally, that heat, above 110 to 120°F, should kill off most weed seeds and root fragments and fibers from regenerating. However, if they survive that or if it’s kept cold and not very actively turned, it will still decompose, but those seeds and those root fragments can lay dormant and then they can resurge once you put them in the garden. So, I would always encourage you to just know your source, be very vigilant about, like I said, when you take weeds out of your garden, know what to put out at the road versus what to compost. I never, under any circumstances, compost any weed material at all, whether that’s a dandelion, a Canada thistle, any other type of weed. It all goes into a bag out at the road. I have enough organic material on-site here that I don’t need to worry about those weeds that could then become a bigger problem later. But just keep that in mind that that tiny little mistake could lead to a big mistake later on and a big problem.
So, hopefully, this helped you guys. Hopefully, you all learned something new. I know it’s probably not the news you wanted to hear; a lot of people want to just have a simple fix, a simple solution. But with some of these weeds, there just is no simple solution, and that’s sometimes how it goes. So, I hope you guys enjoyed; I hope you all learned something new. And as always, this is Luke from the Mi Gardener Channel, reminding you to grow bigger. Take care. Bye.
Hey, thank you so much for reading today’s article.
