Star Thistle

Biological Name:

Centaurea spp. (Star-Thistle)

Natural Habitat:

Star-Thistle: This plant is native to the Mediterranean region, but it has been introduced to other parts of the world, including North America and Australia. It typically grows in disturbed habitats, such as roadsides and fields.


Star-Thistle also known as Centaurea is a plant that is native to grassland and prairie regions of North America. It is a perennial herb that can grow up to three feet tall and it has small oval-shaped leaves and showy pink or purple flowers that bloom in the summer. The plant is known for its sharp spiny burs which can cling to clothing and animal fur and it is often found in disturbed or degraded habitats.

Frequently Asked Questions (FAQs)

Q: Is Star thistle poisonous to humans?
A: Poisonous plants Thus far, only yellow star thistle and Russian knapweed have been implicated in toxicoses in the United States, and only in horses (Panter, 1991).

Q: What happens if you touch thistles?
A: Description: Perennial herb with bright blue flowers and small oval leaves. Health Risks: Entire plant covered in extremely sharp hairs that release an allergen when touched, causing pain, itching, and irritation. Baking soda could be a suggested remedy to symptoms.

Q: Are thistle plants good for anything?
A: Thistle is a very beneficial plant for pollinators. Bees, flies, beetles, and butterflies all like the nectar of the thistle flowers.

Q: Why is thistle a problem?
A: They have become major problems in agricultural landscapes and 22 states have designated them as noxious weeds. Thistles do attract pollinators and birds, but the spiny leaves and stems keep grazers away. Some thistles release chemicals into the soil that inhibit the growth of other plants.

Q: What happens if you eat thistle?
A: Plants frequently grow to five feet tall and prefer plenty of sun. In addition to the root, the stems are edible, when peeled. However, the thistle contains inulin, which gives some people digestive issues.

Q: Why is the yellow star thistle a problem?
A: Yellow starthistle is toxic to horses and causes “chewing disease.” Yellow starthistle seeds can be a contaminant in harvested grain, reducing quality and value. In natural areas, yellow starthistle can substantially diminish native plant and animal diversity.

Q: Is Star Thistle poisonous to dogs?
A: Clinical Signs: The plant is not usually eaten unless other forage is unavailable, or when incorporated into hay. Poisonings occur at ingestions of 50%- 200% of the animal’s body weight over a 60 to 90 day period of grazing.

Q: Is thistle toxic to dogs?
A: If given too often and at too high a dose, milk thistle can also actually cause liver damage and suppress function. This is one of the primary reasons this supplement should not be given to health dogs, but rather only to dogs who have existing liver problems.

Q: Why are thistles hard to get rid of?
A: Because of their tough roots, thistles can be difficult to control. Thistle seedlings have bristles or spines on their leaves, so as soon as you notice a seedling, pull it out before the roots are well established.

Q: How do you get rid of star thistles?
A: Hand pulling or hoeing are most effective in a maintenance program for an area where yellow starthistle is relatively sparse. Take care to remove as much of the taproot as possible. Anticipate that hand removal will need to be repeated in about 2 weeks to remove missed plants or those maturing at a later time.

Q: What animal eats star thistle?
A: Sheep, goats, and cattle can graze on yellow starthistle in early spring, before the flower’s spines develop. Goats will also graze plants in the spiny or flowering stages.

Q: When should thistles be removed?
A: Weaken creeping thistle by repeatedly cutting down the top growth over a number of years. This is best done just before the flower heads show colour as much of the weed’s food reserves will have been used up in flower production.

Q: How do you stop thistles from spreading?
A: If the plant has fully matured, cut them at the base, right under the leaves. Alternatively, use a weeding tool or your hands to pull out the plant by the roots. After getting rid of the thistles, prevent the growth of new plants by spreading a heavy layer of mulch over your garden, or any bare spots in your yard.

Q: How do I get rid of thistles without killing the grass?
A: Heat the thistle roots for a few weeks to kill them off. Then, take a clear plastic sheet and place it over the area. Leave the sheet for 2–3 weeks, then remove it to allow your grass to recover.

Q: Does RoundUp work on thistles?
A: Glyphosate is a non-selective active ingredient found in a number of products (like RoundUp® Pro, Glyfos®, etc.) that are effective in controlling thistle. Glyphosate works well because it is a systemic herbicide that is taken in through the stems and leaves and distributed to kill all parts of the plant.

Q: Are thistles good for wildlife?
A: Thistles provide a succession of micro-environments and food for a range of birds such as siskin and insects feeding on green leaves, flower heads, dead heads and stems.

Q: Why is the purple star thistle a problem?
A: Purple star-thistle poses a dual risk for livestock ranchers; it degrades forage quality by displacing palatable plants and by hindering access to grazing land. Its sharp spines can also injure the eyes, noses, and mouths of grazing animals.

Q: Are thistle weeds good for anything?
A: Thistle is a very beneficial plant for pollinators. Bees, flies, beetles, and butterflies all like the nectar of the thistle flowers. We have these all over our yard here in Maine.

Q: What does Star thistle taste like?
A: Light gold in color, it has a very mild and pleasing floral taste. What makes this honey so incredible is the sweet and persistent aftertaste. It has a distinct aroma of anise (some say almonds), slightly sharp or pungent with notes of sweet, spicy cinnamon, molasses and prune.

Q: Does thistle attract bees?
A: We found that the non-native thistle was the most attractive of the plant species to visiting bee species. However, there was no effect of experimental treatment (presence of thistle) on bee abundance or visitation rate (bees per unit floral area per sample) to native plant species.

Q: Are thistle flowers poisonous?
A: Health Risks: Entire plant is highly toxic to humans and livestock, causing vomiting, diarrhea, respiratory issues, and spasms.

About the author

Samuel is a gardening professional and enthusiast who has spent over 20 years advising homeowners and farm owners on weed identification, prevention and removal. He has an undergraduate degree in plant and soil science from Michigan State University.