What is Canada Thistle and How Do I Control It?

Canada thistle (aka creeping thistle) is a determined weed if ever there was one. An aggressive spreader with spear-like foliage topped with pointy, barb-like hairs, this invader does its very best to intimidate. Sure, it has attractive purple blooms, but don't be fooled. If you spot Canada thistle in your landscape, you'll want to deal with it right away, before it takes over your landscape.

What is Canada Thistle?

While Canada thistle (not surprisingly) grows throughout much of Canada, this weed also thrives in most of the U.S., as well as Europe and Asia. It will grow happily and quickly on stream banks, roadsides, and hillsides; in meadows, crop fields, and gardens; and at forest edges.

Unlike some other insidious weeds, Canada thistle is actually quite easy to spot, especially when it's in bloom. This weed, which can grow up to 3 feet tall, has light green, spear-shaped, serrated leaves covered with sharp barbs. (It goes without saying that you don't want to touch it without wearing protective gloves!) Between June and October, it fancies up its appearance with small clusters of lavender flowers.

There's a good reason Canada thistle has a reputation as a highly invasive, aggressive spreader. It boasts an extensive system of rhizomes (underground stems) that can readily produce new shoots. So, if you disturb the soil and break the rhizomes into pieces, they simply develop into new plants. Canada thistle plants can also produce a lot of seed that can be distributed long distances by wind, water, and animals. Once a population of Canada thistle takes root, it can be really hard to conquer.

How Do I Control Canada Thistle?

The best way to stop Canada thistle from taking up residence in your garden is to routinely inspect your beds for any signs of this unwelcome guest so you can take immediate action when needed. Granted, this weed is also sometimes called "lettuce-from-hell thistle" because of its habit of coming back time and again, but, with persistence, it can be successfully controlled.

Be warned, though: Don't attempt to pull these weeds out by hand, even if you're wearing gloves! Those rhizomes we mentioned above will simply spawn new plants when broken, causing the root system to grow even more.

Here's what to do instead: Use Roundup® Weed & Grass Killer products to kill Canada thistle growing in your garden and landscape beds. The best time of year to do this is either in the spring after they emerge or in the fall when they are preparing to go dormant for the winter. You'll still need to check treated areas routinely for new thistle plants that might emerge from seeds or bits of broken rhizomes. If you spot any, just spray them. Because it's so tenacious, you may have to spray multiple times before gaining complete control over Canada thistle.

Does Canada Thistle Have Any Uses?

While most people familiar with Canada thistle will tell you that it's a good-for-nothing, it's worth noting that the flowers are filled with nectar beloved by pollinators. Still, there are plenty of non-invasive pollinator plants to choose from, so just go ahead and get rid of this menace.

What about Canada Thistle in My Lawn?

With its aggressive ability to spread, there's a good chance this dastardly weed could eventually make its way into your lawn. To control Canada thistle, use Roundup® For Lawns1 Ready-To-Use to spot treat plants as they appear. To prevent future Canada thistle invasions, routinely fertilize your lawn (4 times per year) to keep it so thick and lush that there's simply no room for weeds.