Article written by Lisa Taylor, previous Summit County Weed Manager

For more info on Thistles, check out this Thistles of Colorado Guide
-----

The Good

While many people consider any thistle to be a weed, the truth is that native thistles are anything but a weed.  Their sweet nectar serves as essential food for insects, bees and butterflies. 

Native thistles are used for medicinal purposes and most are edible.  In fact, Native Americans routinely roasted the roots of thistles to supplement their diets.  During the 1870 exploration of Yellowstone, a member of the expedition, Truman Everts, became separated from his group and lost his horse and all his belongings, except for a small knife and a pair of opera glasses.  Due to the lack of means to secure food, Everts survived almost entirely on Elk Thistle roots for over a month until he was rescued (near death at about 50 pounds) by a member of his expedition. 
 
In Middle Park. we are blessed with many native thistles.
 
The Elk Thistle is a plant that is easily found in meadows.  It grows close to the ground and produces a multitude of yellow flowers.  Since it stays so low to the ground it can be easily overlooked.  You can find this plant throughout the high country. 
 
You will find the Mountain Thistle at the higher elevations and above timberline.  As you can see from the picture it seems almost alien.  The flowers are large yellowish or slightly pink in color often “nodding” because of its large size and weight.  This is a very beautiful plant.
 
Like the Elk Thistle, the Eaton’s Thistle can be found throughout the high country.  The plant has clusters of flowers that grow up the stem.  It is sometimes referred to as Frosty Balls. 
 
Lastly, the Fringed Thistle.  This is my favorite!  The white flower reminds me of dog whiskers.  The Fringed Thistle can be found along roadsides and in drier areas. 

Typically the native thistles will be more “hairy” with light pink or white colored flowers.  The stems will often be a reddish color, especially at the base and in the lower stems.  Unlike the noxious thistles which have bright showy flowers, the natives are more muted in color, seeming to blend into the natural environment.
 

The Bad

Middle Park has five thistles that are considered noxious weeds; they are Bull, Musk, Plumeless, Scotch and Canada thistle.   

All of these thistles, with the exception of Canada thistle, are biennials, meaning that they complete their entire life cycle in two growing seasons. 

The first year these plants are in a “rosette” stage, at which time all of the plants energy is put into growing a tap root and large leaves that stay low to the ground. It is during this time that the plant is easiest to control. Simply pop the rosette out of the ground with a shovel and you are done.  

In the second season the plant will shoot up, sometimes to 10 feet tall and several feet in circumference, and will produce flowers that are either pink or magenta in color.  At this stage of the game there is still time to control the plant before it goes to seed.  Again a shovel should be used to dig the plant up, but be sure to wear long sleeves and leather gloves to avoid getting scratched by the thorns.  Chop the plant up and put it in a trash bag, then send to the landfill.  If you just leave it on the ground, the plant will still go to seed and you will have wasted your time. 

Canada thistle on the other hand is a deep rooted creeping perennial.  

Unlike the biennial thistles, this plant does not complete its life cycle after two growing seasons, but continues to grow year after year.   The majority of the plant is underground in its root system, which can grow 18 feet horizontally in one growing season.  Most patches however grow 3-6 feet per year and can easily crowd out desirable species. 

Controlling Canada thistle is much more difficult then controlling biennial thistles.  Although digging or pulling the plant might seem like the thing to do, DON’T!  Disturbing the roots only encourages more growth, and that is the last thing you want.   In mid July, when the plant is flowering, it can be mowed, grazed, cut or treated with an herbicide.  This will kill the top of the plant only, and a followed up treatment with an herbicide is needed in late fall to address the root system.  Because Canada thistle is a tough plant to kill, it can take years of management to finally  be rid of it, but don’t be discouraged, if you are persistent and consistent, success can be had.