Question
We have 2 eleven year old cottonless cottonwood trees out front. This is the first year they are blooming pesty cotton from the top. Why? Is there something that can be done to stop that? We thinned them out 2 years ago could that altered them?

Answer
No Cottonwood trees are either male or female. The females are the ones that produce the cotton seeds. I would say you have a female and the age has gotten old enough to produce seeds. The amount of seed will depend on the weather during the time the tree is flowering and the size of the tree. The less flowers the less seed fluff. There is a chemical that can be sprayed on cottonwood to prevent flowering and the seed.

There is a substance that when sprayed on the tree just prior to flowering will stop the seed from forming. Florel will reduce seed production (cotton). You will likely have to hire a professional arborist to do the job, but it may be worth it to keep from being buried in cotton every spring. Regional timing is important, hence the recommendation for the arborist, plus they have the necessary equipment to adequately cover the trees. Here is a web link to information on Florel

http://www.montereylawngarden.com/info/florel/


Beyond that you may need to think about replacing the tree. Sorry!