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Canada Thistle: Top Weed for Home and Lawn Damage in Colorado

Learn how to identify this weed and how to protect your home.

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There are so many noxious, invasive weeds in Colorado that the Colorado Weed Management Association was founded to focus on invasive species management. The Colorado Department of Agriculture provides a list of 79 noxious weeds along with another 19 weeds that are on the watch list. Given that extensive list, it’s tough to come up with just one weed that’s the worst. However, one does stand out among the others.


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What Is Canada Thistle?

Canada thistle is estimated to infest 129,572 acres across 55 of the 64 counties in Colorado. It overwhelms native plants, builds up around roads, and can dominate lawns.

Each stem produces nearly 1,500 seeds. It grows up to six feet tall, although three to four feet tall is typical. Horizontal roots can spread up to 15 feet and vertical roots grow as much as 15 feet deep. 

As with any rapidly growing plant, the roots of the Canada thistle can find your home’s foundation, entering any cracks and causing further damage. 

How To Identify Canada Thistle

The Canada thistle has dark green leaves four to eight inches long with spiny, serrated edges. It grows in dense strands of multiple plants. 

The branches have three to five white to purple flowers, usually pink, that appear from June to August. The blooms are just under a half-inch in diameter. 

Damage Caused by Canada Thistle

Canada thistle spreads by seeds that can survive in the soil for as long as 20 years. It also expands through its wide-ranging root system, taking over entire areas of your lawn or garden. 

That root growth can find foundation cracks, growing into them, and expanding them further. It can similarly find drainpipes and cause damage there as well.

Once it is established on your property, the critical problem becomes how to get rid of it.

Eradicating Canada Thistle To Protect Your Home

To give you an idea of how challenging it is to eradicate, a fragment from a root just one-quarter of an inch long can form a new plant. That means it’s essential to either remove all roots, which is nearly impossible, or pursue a lengthy program of killing off the weed.

The Colorado Weed Management Association recommends preventing the weed from taking root in the first place. That primarily involves avoiding open patches of soil where the seeds can collect and germinate. Other treatment options include cutting it to the ground, treating it with herbicide, and applying the Canada thistle rust fungus to the plant. 

Perhaps the most straightforward way to deal with an infestation is to consult an expert to fully eradicate the weed and prevent future growth.

We Can Help

If you’re concerned about potential damage to your foundation from Canada thistle, contact the professionals at Complete Basement Systems for a free inspection to ensure the weed has not caused damage to your home. 

Serving Greater Denver area, Colorado Springs, Eastern Colorado, and parts of Nebraska and Wyoming

Colorado Springs, CO

707 County Line Rd.
Palmer Lake, CO 80133

Denver, CO

4686 Ivy St
Denver, CO 80216