Chances are, you've seen this plant along highways and in meadows. Canadian Thistle could be the most highly evolved weed you've ever met. It grows to a height of 4 or 5 feet in a single season. It's leaves are covered with sharp spikes that cut through the toughest garden gloves, making it nearly impossible to remove. Each flower head holds up to a million tiny seeds carried on the wind. These seeds can lie dormant for as long as 40 years, waiting to sprout!
Canadian Thistle is an invasive species that migrated here from SE Asia. It has spread across the entire US, killing native wildflowers wherever it grows. Chemical sprays will kill the Canadian Thistle but that doesn't really solve the problem. Our best defense is to remove the flower heads before they go to seed.