Don’t be fooled by the pretty purple blooms. When you see thistle flowering in your neighborhood, be prepared to soon find it 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 for good.
What Is Thistle?
Although thistle is technically a herbacious 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 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 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. Use this mulch guide to decide what’s best for your garden.
- Snip smart. In lawns, snip small thistle 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 root along with the plant as best you can.
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 spray-of-choice directly on the cut stem. Following are two reliable options. (Whichever you choose, always read and follow label instructions.)
- Horticultural vinegar (30%) provides effective, fast-acting, organic 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. Buy horticultural vinegar now on Amazon.
- Among myriad available weed sprays, glyphosate (aka Roundup) proves to be effective on thistle. Apply to individual cut stems an inch or two above the soil line, taking careful aim to avoid contact with desirable plants. Reapplication in several weeks may be needed for well-established thistle. Check out this great sprayer hack to prevent overspray accidents.