It’s a little late in the season for low-country snow, and yet around this time every year, white fluff wafts through the air, drifts on driveways, gathers in gutters and attaches to any damp surface. The culprit? Cottonwood trees. 

The black cottonwood, Populus trichocarpa, loves sun and wet soil, thriving in the floodplains and riparian corridors of the Puget Sound region. Cottonwoods can achieve centenarian status and attain heights of more than 150 feet. 

While they’re an invaluable part of the natural landscape, cottonwoods aren’t always a welcome guest, writes retired Department of Natural Resources biologist Jim Bottorff. “They sprout when and where they aren’t wanted and form impenetrable stands. They can clog septic drain fields. They are notorious for breaking apart during minor storms.” 

In May and June, cottonwood seeds, shrouded in fluffy white hairs, set sail on the wind and can float for miles before landing and attempting to sprout. News outlets cover the phenomenon almost as regularly as it occurs — the Seattle Times, for instance, published a cottonwood fluff story in 2010 and recycles it every few years. 

The cottony seeds can adhere to wet house paint and clog water intake structures and screens, but are no more than a passing annoyance. While the wind- and water-borne fluff seems like a natural scapegoat when one is suffering seasonal allergies, experts are quick to note the seeds themselves aren’t causing your maladies — cottonwood pollen ran its course in March and April.  

Cottonwood fluff does coincide with peak grass allergy season, according to the Northwest Asthma and Allergy Center, although you may also be suffering from pollen produced by ash, cedar, oak or juniper.

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Julia Tellman writes about civic issues and anything else that happens to cross her desk; contact her at juliatellman@cascadiadaily.com.