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Thistles Are an Invasive Species in Boulder County
Thistles Are an Invasive Species in Boulder County
Yes, it is true, Colorado is home to five invasive-not-so-welcome-thistles. The invasive thistles can be extremely hard on native plant communities. In Boulder County, Colorado, the invasive thistle species of concern include Bull Thistle, Musk Thistle, Canada Thistle, Scotch Thistle, and Plumeless Thistle. These species are considered noxious weeds due to their ability to outcompete native plants, reduce biodiversity, and potentially impact livestock grazing.
If you have thistles on your property and they are left to proliferate, they can spread throughout the community
Here's a more detailed look at each:
- Bull Thistle (Cirsium vulgare)
- Musk Thistle (Carduus nutans)
- Canada Thistle (Cirsium arvense)
- Scotch Thistle (Onopordum acanthium)
- Plumeless Thistle (Carduus acanthoides)
Please, remove thistles from your property to curb the spread of these invasive species. Over the years, they have spread throughout the private properties in the Bar-K and on the Association land. There are many folks in the community that have taken it on as a task to remove them. Please help them by ensuring that the thistles on your own property are not allowed to spread. Thank you!!
Suggestions for How to Remove Thistles
To prevent thistles from regrowing after removal, focus on eliminating the entire root system. This can be done by digging up thistles or using herbicides to kill the root, especially in the fall when the plant is drawing energy into the roots. Repeated cutting or mowing can weaken thistles, but may not completely eliminate them.
Here's a more detailed look at some effective methods:
Digging and Hand-Pulling:
Timing:
The best time to dig or pull thistles is when they are in the rosette stage (before flowering) or during the fall when they are putting all their energy into their roots.
Technique:
Use a shovel or spading fork to loosen the soil around the thistle, then carefully dig up the plant, trying to remove as much of the root system as possible.
Persistence:
Thistles have deep root systems, so you may need to dig multiple times or use tools like a crowbar to get the entire root.
Herbicides:
Post-Emergent Herbicides:
These herbicides kill the thistle while leaving your lawn grass unharmed.Timing:
Fall applications are often most effective, as thistles are drawing energy into their roots at this time.Spot Treatment:
Apply herbicides directly to the thistles, avoiding damage to other plants.Concentrated Vinegar:
Horticultural-grade vinegar (20-30%) can burn thistles, though it may require multiple applications.
Other Methods:
Mulch or Tarps:
Covering thistles with mulch or tarps can smother them and prevent sunlight from reaching the plant, eventually killing it.
Mowing/Cutting:
Repeated mowing or cutting can weaken thistles by preventing them from flowering and setting seeds, but may not be sufficient for complete eradication.
Overseeding:
Thistles are easily outcompeted by other plants, so overseeding can help prevent them from re-establishing.
Important Considerations:
Persistence - Thistle removal requires patience and repeated efforts, especially if you are dealing with a large infestation.
Preventative Measures - Minimize soil disturbance and cover bare soils with mulch to prevent thistles from establishing.
Seed Control - Thistles spread by wind-blown seeds, so if you are dealing with a large infestation, it's important to prevent them from flowering and setting seed.
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