However, it may be found growing under these conditions in a lowered condition. Disturbance is necessary for initial establishment, however, once established it may rapidly spread by both rhizomes and seed. Generally, Canada thistle is not shade tolerant. This may explain why Canada thistle does not persist in tallgrass prairies in good to excellent condition. Extensive rhizomes of Canada thistle make it unique among the thistles.
Rhizomes develop at depths far below the zone of rhizome development for most species.
Most rhizome development occurs in the first 75 cm of the soil, but they have been reported to occur nearly 7 m deep. Lateral root growth of up to 6 m in one growing season has been recorded. With these closely placed buds, root fragments as small as 8 mm in length and 3-6 mm thick have produced new shoots, and root fragments 13 cm in length nearly always produce new shoots. Root fragments can produce viable shoots in as few as 5 days. Root reserves are lowest just prior to flowering, and are the greatest in early fall when aboveground growth stops.