May 22, 2018

The Cottonwood Revelation

There is so much interesting structure to the lower atmosphere that we never see.  Eddies and swirls.  Deflection around buildings.  Large wind speed changes in the lowest few feet above the surface.

Generally invisible, with perhaps a hint evident in the fall when the leaves are fluttering around.

But today everything was revealed.  Every detail. Every nuance of the turbulent airflows near the surface.

The cause of this meteorological boon?  The annual seed dispersal of the region's cottonwood trees.

Every May and early June, during a period when temperatures warm, the seed pods of cottonwood trees burst open, with each seed tied to a good-sized tuft of cotton-like material.   The sky fills with millions of puffs of cotton, each pushed about by the airflow before they eventually reach the ground.

Here are a few videos I took today in my neighborhood today.

Here is a video I found on the web:

I was fascinated by the motions revealed by the tuft of "cotton."   Turbulent eddies of all sizes were evident, as was the weakening of the winds near the surface. 

Slowly the lawns and gardens turned white.

Beautiful, subtle, evocative.


  1. Replies
    1. Fun fact: I learned this week that the Cottonwood fluff blizzard doesn't trigger allergies. It carries the seed, which is non-allergenic. The pollen is released 3 weeks prior, which triggers reactions. Other trees release pollen at the same time of the Cottonwood seed distribution, thus the assumption that the fluff is causing the reaction. I was astounded-- I always timed my rescue inhaler stockpiling to the annual late May snowfall.

  2. I've been able to avoid walking face-first into some rather strategically located cobwebs simply because little tufts of cotton have become embedded in them, making them easily visible.

  3. Cottonwoods were dispersed around the country by a well - meaning but misguided horticulturist, if I'm not mistaken. My family and the county we lived in had many in our yards and our forests, and they were pretty much deemed a nuisance tree by everyone affected. Much like the Blackberry is similarly regarded here in the PNW.

    1. Cottonwood is a native tree and critical to wildlife. The reason it's considered a weedy tree is its rapid growth makes it a weak tree that is a danger and a nuisance in populated areas. Large limbs dropping and aggressive roots invading pipes are some of the issues.

  4. A jar of bubbles or $10 bubble machine can produce this same kind of demonstration. We use this to teach how forests affect wind.

  5. As usual Eric, you are mistaken.
    Cottonwoods are native. Our particular sub-species is populus trichocarpa.
    Fun fact from wikipedia-
    "Trichocarpa" is Greek for "hairy fruits".

  6. @Eric Blair, The genus Populus (poplars, cottonwoods, aspens) is native to North America. Most parts of the USA have one or more native species. Ours are the Black Cottonwood, P. trichocarpa (common) and the quaking aspen, P. tremuloides (uncommon).

    @Rebecca, there's not much in cottonwood fluff to trigger allergies, but cottonwoods do release their seeds at about the same time the grasses bloom, and get blamed for the allergies that are actually being triggered by the invisible grass pollen.

  7. And every year I have to clean off the heat exchanger for our ductless unit after the cottonwoods are done. :)

    I've used a bubble gun to show eddies, etc, to my kids, as well. The little motor can make more bubbles than I can.

    But what I dislike is the fragile nature of the trees. Large, heavy, prone to crashing down for no visible reason.

  8. I have real mixed feelings about the cottonwoods. Trees are nice but these are "weedy" trees. I live next to a cottonwood greenbelt, and the cotton makes a mess of my yard. I even had part of one fluff get in my eye yesterday. Next time it rains the seeds sprout in my gutters. To finish off the show the pods drop onto my deck.

    In a safe place, the fluff can be burned off. It burns fast and completely when dry, but be careful.

  9. Sludulin - I did state that I may be mistaken, but please point out all of the other "usual" times I've been mistaken as well. Should be entertaining.

  10. David B - thanks for the clarification, I stand corrected.

  11. As part of my annual firewise inspection I noticed my attic vents clogged with cottonwood fluff. Not only was this restricting air flow through the attic, it provided "tinder" for a fire to start. A portable shop vac, a ladder and some of my time fixed the problem.


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