What Gender Is Cottonless Cottonwood?

An Icon of America

• One of the tallest trees wherever it grows in the landscape, Eastern cottonwood can reach more than 100 feet tall and have a spread of 50 to 75 feet. It is hardy in U.S. Department of Agriculture (USDA) plant hardiness zones 2 through 9. Plains cottonwood grows to 60 or 80 feet tall and is hardy in USDA zones 3 through 9, and Fremont cottonwood grows 40 to 115 feet tall and is hardy in USDA zones 7 through 10. Cottonwoods grow along riparian areas of rivers and streams. They were a boon to early explorers and settlers, who sheltered beneath them and took cuttings to plant around homesteads to soften prairie winds and provide shade. Meriwether Lewis and William Clark, commissioned by U.S. President Thomas Jefferson to explore the Louisiana Purchase in 1803, fashioned dugout canoes from cottonwoods. It is cottonwoods' ability to root from cuttings that makes it possible to root male cottonwood trees for use as cottonless landscaping plants.

Summer Snowfall

• Female cottonwood trees have 6- to 12-inch-long chains of small green flowers that develop into round fruits that burst and release tiny black seeds embedded in cottony plant hairs. The fluff blows out of the capsules, carrying the seeds some distance away from parent plants. This process happens in June through mid-July in the North and from May through mid-July in the South. In Colorado, the cottonwood fluff turns lawns white. The fluff can clog air conditioners and filters. Some cities have enacted legislation barring the planting of female cottonwoods because of the fluff they produce. Some laws specify the planting of male cottonwood varieties because they don't produce the fluff.

No Fluff but Sneezes

• Male cottonwoods' flowers are 3 to 5 inches long; they consist of tight clusters of round, reddish flowers that bloom in April. They release large quantities of pollen that wind carries to blooming female cottonwood trees. Some cities have laws against the planting of male cottonwoods because of humans' allergies to cottonwood pollen. Some male varieties are "Siouxland" (Populus deltoides "Siouxland") and "Straight Plains" or "Jeronimus" (Populus sargentii "Straight Plains" or Populus sargentii "Jeronimus"). Sometimes cuttings are taken from a male cottonwood and used to reforest wide areas, creating a monoculture.

Possibile Problems Ahead

• In her book "The Cottonwood Tree: An American Champion," Kathleen Cain wonders about the future of cottonwood species' success because of the increased planting of only male clones. The male rooted cuttings are taken from a limited number of parent trees, leading to less variation within the species, and, eventually, fewer females will be available to repopulate the species. In addition, the country has a historic and continuing decrease in natural riparian areas where cottonwoods can re-establish seedlings successfully. Cain calls for a re-evaluation of cottonwood tree management.