By asexual reproduction, it is possible for a colony of entirely male plants to maintain itself. Generally, reproduction from root system contributes to localized spread, while seeds contribute to spread over longer distances. However, some studies have found seeds remain viable up to 21 years and up to 4 months in water. Some studies indicate that the feathery pappus may break off, leaving the seed attached to the parent plant. Seeds mature July-September.
Seeds germinate most readily in mid-spring.
Seeds do not tolerate drought stress or moist, poorly aerated soils, optimal pH range is 5.8-7.0. Competition Disturbance, minimal competition, and adequate light is required for initial establishment. However, once established Canada thistle may readily spread by rhizomes and seed to form single stands. One plant can occupy an area of 3-6' in diameter in two years. Every piece of the root system is capable of forming a new plant.