Weeds in your landscape are bad enough, but weeds that multiply if you pull them up by hand? That’s even worse! Such is the Canada Thistle; if you’re not taking advantage of its useful purposes, it’s a pain to eliminate.
Read on to learn how to manage this thistle effectively while considering its benefits.
What is the Canada Thistle?
The Cirsium arvense is an aggressive and invasive perennial weed. Other names include the creeping thistle, prickly thistle, and cursed thistle. It grows in groups and patches in various soils throughout the US and Canada.
You can find these in open areas like pastures, cultivated fields, forests, and roadsides.
Seeds and Flowers
Each curved or straight seed is ⅒ of an inch long with a cut-off tip and a bump in the center. When growing conditions aren’t present, the seeds can persist in the soil for over 20 years before germinating.
From summer to early fall, multiple pink or purple pom-pom-shaped flowers bloom on inch-wide heads, surrounded by wooled bracts. The male flower is smaller and rounder, while the female flower is fragrant. When they go to seed, they become white and fluffy like dandelions.
Stem and Leaves
The slender and grooved stem grows upright at 1–5 feet tall with a branching habit at the top.
On the stem are 2–8-inch dull and soft green leaves. When young, they’re thick and egg or spear-shaped with wavy-lobed, thorny edges and short, bristly hair. Their shapes are similar, irregularly lobed, and still thorny when they mature.
Brief History of a Cursed Thistle
Just because Canada is in its name, that doesn’t mean this creeping thistle originated there. It got its name when early New England residents blamed French traders from Canada for the weed’s presence.
The Canada Thistle is believed to have come from the eastern Mediterranean region. It could be the first weed that early settlers brought to the US.
What Makes the Canada Thistle a Weed?
Over three to five years, the thistle forms a colony of weeds through its aggressive propagation. The thistle stores its food energy in its root system to survive winter. During the spring, it produces about 1,500 seeds per shoot.
Spreading like a Hydra
One spreading habit makes this weed earn the name creeping thistle. It doesn’t just spread by letting the wind carry the feathery seeds to other areas.
Growing downward 6 feet and spreading out 15 feet as rhizomes (or rootstalk), those aren’t individual weeds on the surface. They’re all connected, and if you pull them up, two more weeds grow from the split rootstalk like a hydra. Talk about a mythical underground network!
Issues and Damages Caused by Canada Thistles
The Canada Thistle is a noxious weed that crowds out native plants and reduces rangeland quality. As a perennial weed, it will cause severe crop-yield losses to your perennial crops, like wheat and barley.
Fortunately, this prickly thistle isn’t toxic, but it’s painful if you step on it without shoes or grab it without gloves. Should it stick to you, take it out with a pair of tweezers.
Managing Canada Thistles
Managing the Canada Thistle means you’ll have to do it for years due to its resilient root system. Combining control methods and employing them when the weed is young are keys to managing this cursed thistle.
Environmental Stresses and Shade
Floods, droughts, and cold temperatures will stress the Canada Thistle enough to suppress its growth and eventually kill it. And since it needs direct sunlight, try planting a large crop like alfalfa to block the sun from the thistle.
Snipping the Bases
You can make a clean cut at the thistles’ bases with sharp scissors or a lawn mower. The idea is to avoid splitting the roots so the hydra can’t multiply its heads. Though it’s a repetitive process, it exhausts the weeds’ energy, so they’ll eventually die.
Use herbicides that affect the roots. Apply them when the temperature is 65–80 degrees, and for non-selective herbicides, avoid windy days. Whether you use a pre- or post-emergent herbicide, always check your yard if reapplication is necessary.
Preventing the Thistle’s Return
After eliminating the thistles (or before they ever grow), take some yard-maintenance measures to keep your lawn healthy and weed-free.
Watering your yard well with an in-ground sprinkler system is one way. Another way involves annual core aeration to allow water, nutrients, and oxygen to flow easily in the soil. And if you see any thinned areas, plant grass seed so the creeping thistle has no room to grow.
Beneficial Uses of Canada Thistles
Other than existing as food for pollinators like bees and butterflies, there is some good to this prickly thistle.
Despite their painful appearance, the leaves of the Canada Thistle are edible. When harvesting, wear gloves and thick clothing. After slicing off the thorns, crush the leaves for juices and tea blends.
To eat the flower buds, harvest them before they go to seed so you won’t eat a bunch of fluff. Cook and peel them like you would an artichoke.
The stem and roots are best peeled, shaved, and roasted or boiled, but only before the flowers bloom. You can eat them in vegetable dishes and, like the leaves, prepare them for tea blends.
The roots have mildly astringent properties; you can use them to treat dysentery and diarrhea once their acute symptoms pass.
When the leaves are boiled in water and ingested, they make milk flow smoothly for mothers and overcome hepatic obstructions. They also help soothe irritable sores and eyes (after you remove their thorns).
Wrapping Up the Canada Thistle
While good for eating and treating, it’s best to avoid dealing with the Canada Thistle if possible. It’s not easy to do away with this cursed thistle, but it’s possible with effort, repetition, and commitment.
If you feel like you need to learn more about these pesky garden tenants, check out our weeds page to learn all about different weed varieties, treatment options, and surprising information.
- About the Author
- Latest Posts
With a lifelong appreciation for the vibrant hues and serene beauty of landscapes, Sarah Keck brings a wealth of practical and observational gardening knowledge to her writing. Her hands-on experience stems from years of assisting her mother in tending a diverse array of plants, mastering the art of plant care through careful adherence to proven horticultural practices.
A seasoned observer, Sarah delights in the study and admiration of flourishing flower gardens and lush greenery during her frequent strolls through local parks and the quiet streets of her neighborhood. Her natural curiosity drives her to investigate various plant species, deepening her understanding of the flora she encounters.
In addition to her botanical pursuits, Sarah cherishes the culinary arts, drawing from her college experiences of handling and preparing fresh produce. Her penchant for discovery leads her to continually refine her methods, which she eagerly documents and shares with fellow gardening enthusiasts.