Please note: The WHO considers glyphosate to be a probable human carcinogen. Its use is prohibited in some states and countries. Please check with your local laws and wear gloves, sleeves, a dust mask, and goggles if you apply it. Do not allow any pets or livestock to wander into the area while it’s being treated. [4] X Trustworthy Source Penn State Extension Educational organization dedicated to delivering science-based information to people, businesses, and communities Go to source You may need to do this multiple times. If the thistles grow back, treat them again. It can take a few seasons to completely remove the weeds. Unfortunately, glyphosate is some pretty strong stuff. This herbicide will kill any plants it comes in contact with, so you may have kill off some innocent bystanders when you go this route. However, if your thistles aren’t located in a garden, it may not matter much to you. [5] X Trustworthy Source Royal Horticultural Society Leading gardening charity in the U. K. providing resources for identifying, growing and caring for flowers and other plants Go to source
Combining a selective weed killer with competing plants is one of the most efficient combos when it comes to getting rid of thistle. [7] X Research source Don’t assume that your weed killer isn’t working if the thistles grow back after you’ve killed the visible plants off with your weed killer. So long as you keep at it, if the seeds can’t spread and the shoots can’t flourish, the roots will slowly die out over time.
When it comes to grass species, alta tall fescue is the most effective, while Troy bluegrass is the least effective at competing with thistles. [10] X Research source Over years, this may actually completely get rid of your thistle problem, but it is definitely a long-term solution. There’s always the possibility that the thistles continue to thrive, though.
Clean your tools thoroughly after you’re done using soap and water. If there’s even a single seed sitting on a tool and you use it elsewhere, the thistles may reappear. Thistles have deep root systems, so this can take some effort. It’s key that you remove as much plant material as possible, though. Thistles can regrow out of basically any part of the plant, so you can’t leave any scraps behind. [13] X Research source
The best time to start this process is after the thistles have grown rapidly and you see the bulbs forming on the stalks, but before the plants have actually flowered. If you start this process at this point, you won’t need to worry about seeds spreading around. [16] X Trustworthy Source EDIS Electronic database of the University of Florida Institute of Food and Agricultural Sciences’s peer-reviewed articles Go to source It helps to combine this process with a weed killer of some kind. You’re likely going to have to mow multiple times over the course of several growing seasons to fully remove the plants.
Don’t till the soil in the growing season if you can’t pick up every piece of thistle you tear up, since tilling may accidentally spread seeds. If it won’t be hard to pick everything up, feel free to do this during the growing season. It may take multiple attempts, though.
The thistles may grow back if the roots didn’t completely die out while you covered the plants, but this is a pretty low-effort option so if this doesn’t work, at least you didn’t spend much time or energy on it! Overlapping layers of cardboard can also work well for this. [19] X Expert Source Ben BarkanGarden & Landscape Designer Expert Interview. 14 April 2020. You can also try solar sterilization, where you place layers of plastic or landscape on top of the weeds. The cover will block the sunlight from the plants and kill them using the heat of the sun. [20] X Expert Source Ben BarkanGarden & Landscape Designer Expert Interview. 14 April 2020.
The livestock won’t totally remove the thistles, but this is a solid way to keep the problem under control while you’re dealing with the issue in other ways. Just don’t let your livestock snack on any thistles you’ve chemically treated. Chickens may snack on thistles, although some poultry farmers claim that they aren’t good for chickens. Unfortunately, there isn’t a ton of research out there on this. Thistle can be toxic to some livestock, although it’s rare that the animals will eat enough of it to cause any harm. Still, just to be safe, make sure that any livestock have other options available so that they aren’t eating a diet consisting of 100% thistle. [24] X Research source
Your thistles will likely grow back relatively soon. Keep repeating this process until they’re totally gone. The root system should dry out and die after several growing seasons. Thistles are pretty persistent, and standard white vinegar isn’t particularly potent—usually it’s 5% vinegar. If possible, pick up some industrial-strength 20% white vinegar and use that. [26] X Research source You may need to reapply the vinegar after it rains.
Once the thistles are dead, throw on some gloves, pick up any remaining plant matter, and stuff it in a garbage bag. Throw the thistles out along with the rest of your trash. Urophora cardui, also known as the thistle gall fly, is another option that will feed on thistle plants. Unfortunately, it can be kind of tough to purchase them, though. [28] X Research source Unless you’re going for a super organic and natural solution, this may not be the most efficient solution. The bugs will often leave if the larvae hatch and there aren’t enough thistles to snack on, and your thistles may grow back after the bugs have all moved on.
