How Often Do Eastern Cottonwood Tree Drop Seeds?
- Eastern cottonwood trees are either male or female, based on the floral organs present in their flowers. Only female trees develop seeds that are shed later. Male flowers are reddish and more conspicuous in 3- to 5-inch long pendent clusters called catkins. Pollen from the stamens on male blossoms scatter in the wind. Greenish female flowers occur in catkins measuring 6 to 12 inches long. When pollinated, one female blossom can yield 30 to 60 seeds in a capsule.
- About two months after cottonwood trees bloom, the fluffy seeds release into the wind for dispersal across the landscape. Progressive release of seeds into the air can last as long as eight weeks on each tree. Flowering time and release of seeds can vary among female trees, so if multiple trees exist in a grove, they may not necessary bloom and cast seed cotton at the same times. In the northern part of its natural range, cottonwood trees drop seeds from June through mid-July, and from May to mid-July farther south, creating a longer "cottony snow" effect to the air.
- Cottonwood trees can begin flowering and producing seeds anytime between five and 10 years of age. As the tree ages and attains more size and branches, the number of flowers and seeds increases exponentially. A mature female tree can yield more than 40 million seeds annually, according to the U.S. Forest Service. With such vast numbers of seeds, the long shedding period may create an effect of multiple crops of seeds. When it's not windy, seeds drop close to the tree, often unnoticed by people. Windy days scattered over several weeks create an illusion that the cottonwood tree is releasing seeds in separate events.
- In a garden setting, eastern cottonwood trees are often considered to be messy trees because of their seeds as well as their expansive, water-seeking, fibrous root systems. Wild cottonwoods are often retained on edges of property as an inexpensive windbreak, screen or source of shade. To avoid the dispersal of cottony seeds, plant either of the male cultivars "Nor Easter" or "Siouxland," which are propagated by cuttings. Growing cottonwood from seed leads to an unknown plant gender until the tree first blooms.