Killing Thistles for Good From Master Gardener David Wall

June 2, 2024 – Thistles are a great attraction for pollinators.  The flowers are very attractive, and the plant has several medicinal qualities. On the other hand, they’re as tough a weed as you’ll find anywhere.  Their tap root is known to go down as far as over 15’, and it annually puts out many thousands of ultralight seeds.

When living in the country, I used to go out with a hoe and chop them down, which really amounted to nothing more than keeping them in check, because even chopped down, that tap root will bring them back, and who wants to dig that far down to get “all” the tap root.

Fortunately, there’s an organic, effective, and easy way to eliminate thistles.  Horticultural vinegar kills the above ground plant and the below ground taproot.  Local feed stores should have it or be able to order it for you. 

Vinegar you buy in the grocery store is usually 3-5% acid.  Horticultural vinegar is a stronger version, weighing in at anywhere from 15-50% acidity.  For regular weeds, I use 30% diluted with water to 15%. For thistles, a minimum of 30% is needed, but 35-45% is best.

For garden use, I use a handheld spray bottle, get right next to the weeds, and lightly spray. You don’t want to “generally” spray, because the mist will kill whatever it touches.  A similar, but more pinpoint method is used to kill thistles.

With a good pair of garden shears or scissors, cutdown the thistle no more than a few inches above ground.  Immediately use a small spray bottle or even an eye dropper, to get the vinegar directly on the exposed cut.  The plant will attempt to seal the cut and readily allow the vinegar to penetrate the plant veins and be carried down the tap root.


Author: Matt Janson

Share This Post On