Gardening with Deb Babcock: Thistle harmful to environment and animals |

Gardening with Deb Babcock: Thistle harmful to environment and animals

Deb Babcock

Thistles are not simply a problem for tender feet, they're actually harmful to our environment and our animals.

When I was a little girl, I had to be careful going outdoors barefoot in the summer because our yard had sharp plants in it that I called “pickers.” Now as an adult and a Master Gardener, I’ve learned that these weeds are thistles and they are not simply a problem for tender feet, they’re actually harmful to our environment and our animals.

Canada thistle (Cirsium arvense), for example, is an aggressive, non-native species that is invading pasture land and meadows in Routt County. Its seeds are carried to our properties via streams and rivers, in hayseed and on equipment that has been used in infected areas.

Besides being somewhat unattractive and painful to rub against when hiking (or walking around barefoot) due to its sharp barbs, this invasive weed reduces range land for stock and wildlife because animals tend to avoid grazing in areas with thistle.

One thistle plant can spread to a 3- to 6-foot area in just one to two years, so it is important to keep infestations down before the plant takes over an entire meadow. It’s a tough one to kill since its horizontal roots can grow to 15 feet across and vertical roots go down 6 to 15 feet deep. If the entire root isn’t eliminated, this plant easily regenerates from root particles as small as a quarter inch.

As the daylight hours become longer, thistle plants begin to flower, producing about 1,000 to 1,500 seeds per flowering shoot. These seeds remain viable for as many as 22 years if they land into the soil and become buried.

The key to eliminating thistle in your yard and meadow is to stress it out. Continual cutting and digging of the plant and root system weakens the plant as it returns again to its root system for energy and nutrients. To eradicate it, you’ll need to work at it throughout several years.

Recommended Stories For You

Growing grasses or alfalfa will help keep thistle population down since the grass roots will complete with thistle for space and nutrients. But grass alone isn’t enough, you’ll need to supplement this method of managing thistle with other controls.

If you prefer chemical controls, research at Colorado State University shows that Tordon 22K (picloram), Milestone (aminopyralid), Transline (clopyralid), Perspective (aminocyclopyrachlor + chlorsulfuron), Banvel/Vanquish/Clarity (dicamba) and Telar (chlorsulfuron) are effective against Canada thistle. Be sure to read the label when using these herbicides to get the best results.

There also is a biological control that has proven effective in controlling thistle. Ceutorhyncus litura is a weevil that feeds on thistle, eventually killing the plant, but it needs to be used in conjunction with other management methods.

Canada thistle is distinguished from other nasty thistles such as bull thistle (Cirsium vulgare), musk thistle (Carduus nutans) and Scotch thistle (Onopordum acanthium), which are biennial plants, because Canada thistle has multiple small flowers and smooth stems between the leaves. The bull, musk and scotch varieties have one long tap root and propagate more by seed than root. The flowers on these other thistles turn into seeds that have small “umbrellas” on them like dandelions and are carried on the wind. So it is important to catch and remove these other thistles before the flowers turn to seed and get dispersed.

Deb Babcock is a volunteer Master Gardener through the CSU Extension Routt County. Products mentioned in this article are not endorsements but simply provided for information purposes. Call 970-879-0825 or email with questions.

For more

For more information about noxious weeds and how to manage them on your property, stop at the Master Gardener booth at the Farmers Market on Saturday and talk with the volunteers on hand. They have fact sheets and other materials to help you.

Go back to article