The greatest flush of root-derived plants occurs in spring, but another flush occurs in fall. A flush can occur anytime during the growing season when moisture is adequate. This is particularly a problem when Canada thistle growth is disturbed by tillage or herbicides. This feature can be manipulated to the land manager's advantage. Plants that germinate from seed do so at about the same time as root-derived shoots.
Seedlings grow slowly and are sensitive to competition, particularly if shaded.
Reproduction and spread. Female flowers produce a sweet odor and Insects readily pollinate different sexed patches up to 200 feet apart. Canada thistle develops seed sparingly. It may produce 1,000 to 1,500 seeds per plant. Generally, vegetative reproduction from its root system contributes to local spread and seed to long distance dispersal.