Cotton Thistle
Onopordum acanthium
Last reviewed: August 2026
Toxicity unknown
Cotton Thistle (Onopordum acanthium) is not listed by the ASPCA Animal Poison Control Center (opens in new tab) or the other sources we check, so we have no verdict for it either way. Absence from those lists is not a clearance. If your pet shows symptoms after eating any plant, call the ASPCA at (888) 426-4435.
Light
full sun
Water
low
Size
36"–72" H × 24"–48" W
Bloom
Jun, Jul, Aug
Pollinators
bees, butterflies, beetles
Native alternatives to Cotton Thistle
Cotton Thistle is not native to the United States. These natives fill a similar role in a planting, matched on bloom season, bloom color and mature size.
Before you buy
Your city may pay you to plant this
Cities and water utilities offer rebates for replacing lawn with native and water-wise plants. We track 452 programs across 44 states, each with a link to the provider and the date we last checked it.
Find rebates in your areaCotton thistle is a tall, imposing biennial with large, spiny silver-green leaves and purple thistle flowers that bloom through summer. This dramatic plant can reach 6 feet tall and forms a striking architectural presence in the landscape. It self-seeds readily and tolerates drought conditions once established.
In an HOA neighborhood
Cotton Thistle takes more care to keep looking intentional in a front yard. Maintenance level: moderate. Consider it for backyard or mid-zone beds rather than the street edge.
Works well in: backyard only.
- Extremely tall and can appear weedy
- Sharp spines pose safety concerns
- Self-seeds aggressively and may spread
Wildlife value
The large purple flowers attract bees, butterflies, and beetles during the summer blooming period. Seeds provide food for finches and other birds in late summer and fall.
Common questions
- How much sun does Cotton Thistle need?
- Cotton Thistle grows best in full sun conditions.
- When does Cotton Thistle bloom?
- Cotton Thistle blooms in June, July, and August.
- What pollinators does Cotton Thistle attract?
- Cotton Thistle draws bees, butterflies, and beetles.
- Is Cotton Thistle HOA-friendly?
- Cotton Thistle takes more care to look intentional in a front yard. Consider it for backyard or mid-zone beds rather than the street edge.
Pollinator and host plant associations compiled from GBIF, iNaturalist, and published ecological literature.
If something looks wrong
Common plant problems, and what to check first
These come up on almost any plant. Each guide lists the likely causes in the order they are worth ruling out, with one thing to check before you act on any of them, and links to the source it came from.
- It is dying right after planting
- Leaves turning yellow
- Wilting even though I watered it
- Brown crispy leaf tips
- Bugs on the plant
Ready to grow Cotton Thistle? Add it to your garden in Pollinator Patch to track it and get season-by-season care guidance.
Planning a bed around it? Start a free plan with this plant
Not sure where to start? Take the 2-minute yard quiz