Soil Cottonwood grows primarily on alluvial soils of the bottom lands. The soils are in the orders Entisols and Inceptisols. Male flowers are only 8 to 13 cm long. They have 40 to 60 stamens and are reddish in color and more conspicuous than female flowers. Female flowers elongate to 15 to 30 cm.
Males tend to flower a few days earlier than females.
Trees have flowered as young as 4 to 5 years old. Seeds develop 30 to 60 per capsule on short stock on long catkins. Each capsule has 3 or 4 valves. Seed production starts when tree are 5 to 10 years old, increasing rapidly in amount as the trees become older and larger. Estimate of annual seed production of a single open-grown tree is as high as 48 million seeds.