You're heard the saying about a weed being any plant growing where it isn't wanted? I can tolerate a variety of "weeds" in a lawn, but thistles are not one of them. Thistles are frustrating if you're trying to have a kid friendly lawn - what kid wants to walk barefoot on a prickly thistle? Not mine. So, what to do. I don't want prickly weeds for my kids to step on but also don't want to use potentially dangerous chemicals on the lawn.
Here is one approach I've been using over the last year with good success. It's a little unorthodox, but if you're stuck between a thistle and a chemical, it might just be worth a try for you.
Yes, it's a little strange to use a syringe for organic weed control, but stay with me here. There are a variety of places online that sell syringes...here's a 10 ml syringe that will work well available from a website I used.
Adios Organic Weed Killer is a newer organic weed killer that works better than others on thistles. There are a lot of organic weed and grass killers out there (like Burnout Organic Grass & Weed Killer) that work great at killing the above ground portion of plants but don't work so well at killing the roots.
Burnout is perfect for spraying on weeds in your mulch beds and sidewalk cracks etc. but isn't ideal for spraying in the lawn. Adios has some degree of an ability to travel into the plants root system and be absorbed giving it a much better chance to kill the entire plant, rather than just the above ground portion.
I've used the Adios Concentrate in my trials to date, but you might be able to get the same results with the ready to use Adios - I'll try that next.
Mowing should cut the top off the thistle and expose the stem. If it doesn't to this, you can break off the top with your hand (heavy glove recommended). Just try to weed it without pulling out the entire root.
After you've cut the grass, get out your Adios and your syringe and fill the syringe with Adios by sucking it either directly out of the container or by pouring the adios into a bowl and sucking out of that.
Insert the syringe needle into the stem of the thistle as far as you can and slowly push in the plunger to release the Adios into the stem. If you pull the syringe out slightly as you press in the plunger, it will allow the adios into the stem more easily. I usually do this twice on each plant.
Go ahead and spray the leaves and into the stem with a ready to use Adios mixture to make sure you're getting as much adios into the plant as possible. You can mix a batch of concentrate in a pump sprayer or just use a ready to spray bottle like the one pictured below.
This is the fun part. It will take some time. If it doesn't seem affected after a week, try a reapplication. This isn't a magic bullet, but it can be really effective and is a much better tool to get rid of thistles organically than we've ever had.
Thistles have a very invasive root system which is one reason why they are so difficult to get rid of. The ideal time of the year to do these injections is in the late fall when the thistles are pulling all their energy into their roots - they'll pull the Adios into their root system most effectively when this is happening in the fall. The thistles I injected this way last fall have yet to return and it's already July, so the results look very promising. I have done some this summer that have not returned yet, but I won't be surprised if they do and I need to do a reapplication this fall.
So, if you're trying to get rid of thistles, the best organic way I know of to do it is to inject Adios directly into the stem.