FAQ

Male clones of cottonwoods should not produce cotton- only the female trees produce the seeds ("cotton").
Sometimes you will hear of cottonless cottonwood trees later developing cotton but they were probably mislabeled.
Some hybrid cottonwoods sold are listed as "sterile female hybrids."  These are not cottonless because they are not male.  The "sterile" refers to the fact that the seeds they produce are incapable of germinating.  However, they still produce the cotton to distribute the seed.
If you have a cottonwood that produces cotton and you don't want to cut it down, you can use Florel  to prevent cotton development in female trees.  You will need to check the label to see when to apply it.