Seeds germinate almost exclusively on the freshly deposited, exposed alluvium left by receding floodwaters. Root growth of young Fremont cottonwood seedlings is very rapid on favorable sites. Because the upper layers of the moist alluvium dry rapidly with the onset of warmer summer temperatures, rapid root growth is essential in order to reach depths where a supply of water is available. P. f. ssp. In general, Fremont cottonwood 1st flowers early in the spring, before leaf emergence, and finishes by the end of May. Seed drop roughly coincides with the receding of spring floodwaters.
Cottonwoods are dormant during the fall.
Leaf senescence occurs in late September and abscission in mid-October.