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Canada Thistle: Top Weed Damage in Western Colorado

Canada thistle is an invasive plant that can cause damage to your western Colorado property. Learn how to identify it and how to protect your home and foundation.

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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 tops the list for home and lawn damage throughout western Colorado. We’ve selected Canada thistle.


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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. This noxious weed overwhelms native plants, builds up around roads, and can dominate lawns.

It grows up to six feet tall. Two to four feet tall is typical. Horizontal roots can spread up to 15 feet and vertical roots grow six to 15 feet deep. Each stem produces from 1,000 to 1,500 seeds. It’s been found at altitudes as high as 12,000 feet.

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 stands of multiple plants. 

It flowers in late spring and throughout the summer. The flowers form small clusters of one to five flowers, roughly 3/8 inch across, and vary from white to pink to purple.

Damage From 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. A one-quarter-inch fragment of root can form a new plant.

That root growth can find foundation cracks, growing into them and expanding them further. It can also find drainpipes, clogging and cracking them.

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

Eradicating Canada Thistle To Protect Your Home

Since 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.

Ideally, you’d do all you can to prevent the weed from taking root in the first place. That means watching for growth in areas adjacent to your lawn and avoiding disturbing your soil where the seeds can take root.

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, contact the professionals at Foundation Repair of Western Colorado for a free inspection to make sure the weed has not caused damage to your home. 

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2575 U.S. 6 & 50, Unit A
Grand Junction, CO 81501