How to Get Rid of Thistle Weeds for Good

Don’t be fooled by the pretty purple blooms. When you see thistle flowering in your neighborhood, be prepared to soon find your neighbor’s weeds in your lawn and gardens. If it’s already there, take heart. With persistence and these proven methods, learn how to get rid of thistle weeds for good.

What Is Thistle?

Although thistle is technically a herbaceous plant of the daisy family, it’s also classified as a Noxious Weed in many states, meaning it’s harmful enough to warrant government-regulated control. The most common thistle species, Canadian or creeping thistle (Cirsium arvense), is a lawn weed found throughout the U.S.

Good to Know, How Thistle Grows

That innocent-looking thistle flower matures into a seed-producing machine. Each can produce between 1,500 and 5,000 seeds that take wind and populate. Once seeds land in your lawn or garden and germinate, they send out spreading roots (rhizomes), which can extend up to 20 feet away from the plant, and many feet deep, in the right conditions.

Just spotted thistle blooms in your yard? Remove the flowers immediately, bag them, and place them in the trash. DO NOT compost! Also: Dry, open and uncovered soil is like a thistle welcome mat. Consider laying down a weed barrier or mulch to slam the door on new infestations.

How to Get Rid of Thistle

Being a perennial, thistle can live for many years. Seedlings and new plants are easiest to kill, but take heart: There’s hope for beating mature ones as well. Stick with it to get rid of thistle for good.

Seedlings and Small Plants

• Plant prolifically. Thistle seedlings germinate in empty, unshaded soil. Pulling them may leave a portion of the root behind, which will re-sprout in time. In your flower or vegetable garden, plant densely around the thistle. As your chosen plants mature, their shade ultimately weakens and kills the sun-loving baby thistle weeds.
• Cover it. Mulch eliminates thistle seed germination and smothers new plants. Use it around new plants as they gain size, and cover vacant soil.
• Snip smart. In lawns, snip small thistles at the soil level. While mowing prevents it from maturing, it does not kill it. Snipping must be done regularly to eventually weaken and kill the small plant. (This is for the random thistle, not a large infestation.)

Dig Them Out

Remember the part about rhizomes? They make digging thistle from your garden or lawn tricky, since one mature plant’s roots may wander into your neighbor’s yard. However, it is an effective way to remove larger plants. Use a sharp weeding tool to get down into the soil, removing roots along with the plant as best you can. Manual weeding tools are effective for single plants but don’t make the mistake of hand weeding an entire lawn.

Break Out the Spray

Eventually, you may have to spray. This is especially true with mature, blooming-sized plants and large infestations. Start by cutting mature plants off an inch or two above soil level, then apply your weed killer of choice directly on the cut stem. The following are two reliable options. (Whichever you choose, always read and follow label instructions.)

• Horticultural vinegar (30%) provides effective, fast-acting, organic weed treatment. Be aware, however, that this caustic acid should be used with care, like any other spray. It is appropriate for spot-spraying individual plants, not entire areas. Because it’s an organic acid, it can change the soil pH, so avoid applying it in vegetable gardens or around sensitive plants.
• Among the myriad of available weed sprays, glyphosate proves to be particularly effective on thistle. Apply to individual cut stems an inch or two above the soil line, taking careful aim of the weed sprayer to avoid contact with desirable plants. A reapplication in several weeks may be needed for a well-established thistle.