How to Get Rid of Thistles Growing Through Shrubs

We have Sandy in Plain Township. ‘I have a weed, thistle, growing through my boxwoods and one azalea. What is the best way to get rid of it? Do I cut it? Do I try to pull it?’

That’s going to be a tricky one. If it’s in the very center of the boxwood, you’re probably going to have to get down there and pull it out by as much of the root system as you can get. It probably will come back.

If you can catch the plant when it’s young and really close to the ground, and you can use a piece of cardboard and block off the boxwood part and only put Roundup on the thistle itself, then you could kill the thistle without hurting the boxwood. I’ve seen people take it and dip a paintbrush in it and actually paintbrush it on the leaves. That way they don’t drip it or get it onto anything, because whatever foliage it touches, it’s going to kill.

So the best way to do that is to try to use a systemic so you kill the root system of that plant. Same thing with the azalea. You don’t want to get any of the Roundup on the azalea or the boxwood, you just want to get it on the thistle. And when the thistle grows up through the plant, you really can’t treat it above the plant. So if you tear it off at the ground, get as much of that root as you can, you’re not going to get all of it. It will start to come back.

But down at the base, sometimes as it starts to peek back through in a week or two, you can just paintbrush the leaves of the thistle and it will draw it down into the sap system. It’ll through the sap system will draw down to the root system and kill the root off that way. That is a tricky, trickier problem. Yes, it is. So then get the Roundup and put it now when it’s showing or underneath the boxwood.

You’re going to have to get down and get down to the bottom. And just as it starts coming back from the ground, when it’s young, you’ll see most of the time the thistle is not in the center of the boxwood, it’s off to the side. But when it grows, it’ll force its way up through the center.

So when you tear out the old one, when it comes back, it’s going to be off to the side of the boxwood. And you just want to get down there and just paintbrush the leaves on that thistle. That way it draws back down to the root system. Just do not get that Roundup on any of the foliage of the boxwood or the azalea. It won’t hurt if it touches the ground. Just don’t want to get it on the foliage.