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Bull thistle flowers. Photo Credit: Alex Katovich, Bugwood.org -
Bull thistle flowers. -
Bull thistle flower. Photo Credit: Kenneth M. Gale, Bugwood.org -
Bull thistle leaf. Photo Credit: Steve Dewey, Utah State University, Bugwood.org -
Bull thistle rosette. Photo Credit: Michael Shephard, USDA Forest Service, Bugwood.org
Also known as: Fuller’s thistle, common thistle, spear thistle
Bull thistle is a widespread biennial plant that can be found throughout North America. Although it is intimidating in appearance, it is not as challenging to control as other thistles and is mainly a problem in hay fields and pastures.
Description:
| Life Cycle: | Biennial (life cycle lasts two years) |
| Early Detection and Rapid Response species: | No |
| Height: | Up to 6 feet (2 meters) tall |
| Leaf Description: | During its first year, bull thistle forms a rosette with green leaves. These leaves have deeply lobed edges and a sharp spines at its tips. During its second year, it has similar leaves that grow alternately along a flowering stem. |
| Fruit & Flower Description: | Flowers are dark purple and grow in gumdrop-shaped flowerheads. Flowerheads may occur by themselves or in clusters of two or three. It only spreads by seed. Each flowerhead can produce up to 700 seeds. |
| Bloom Time: | June to October |
Habitat:
- Bull thistle is commonly found in pastures, logged forest areas, hayfields, and along roads.
- It prefers sunny, open areas but can tolerate a wide range of soil conditions, from moist to dry.
Impact:
- Bull thistle outcompetes native plants and desirable forage plants.
- Monocultures in pastures inhibit livestock movement and interfere with grazing.
- In recently logged areas, it reduces the survival of tree seedlings.
- Its presence can cause hay prices to decline.
What you can do about it:
- It reproduces by seed so preventing seeds from spreading is key to stopping new infestations.
- Contaminated hay is a primary means of spreading seeds. It’s best to purchase certified weed-free hay.
- For smaller patches, hand-pulling individual plants can prevent further spread. Digging is easiest in the spring before the plant flowers.
- For flowering plants, remove any flowers or seeds and place them in a tied plastic bag before you dig the plant up. Make sure to throw the plastic bag away in the trash – not the yard debris or home compost.
Look-alikes:
Bull thistle looks similar to other invasive thistles, including creeping thistle (Cirsium arvense). Bull thistle’s flowerheads are larger and the spines at the tip of its leaves are more pronounced than creeping thistle’s.
Noxious Weed Listing:
| State of Oregon: | Class B |
| State of Washington: | Class C |
More Resources:
Download the Bull Thistle Best Management Practices Factsheet
- Pacific Northwest Weed Management Handbook: Bull thistle
- University of California, Weed Research & Information Center: Bull thistle