Ask a Naturalist– What’s that fluff?

c-cottonwood fluff


Q: It’s June—why does it look like there’s snow on the ground?

On the opposite side of the year’s wheel from the chill of January, on a warm, fresh day in early June, you may experience a moment of cognitive dissonance: it’s snowing? Of course, it is not snow, but the other fluffy white stuff that falls from the sky: the seed of the eastern cottonwood (Populus deltoides), otherwise known as cottonwood fluff.

This time of year, many people are complaining about cottonwood fluff. It goes everywhere, settles and drifts in inconvenient places, covers cars and decking, and clogs gutters and drains. Then when it rains, all those tiny fluffy fibers get practically plastered into place, causing cleanup headaches. These fluffs, carried on the wind, are also frequently blamed as the culprit for seasonal allergies; even though cottonwood pollen is long gone by the time the fluff shows up. So complain all you like about blocked gutters, but don’t blame the cottonwood for your June sniffles!

If we move past the annoyance that the fluff can cause, which really only lasts a couple weeks, there is so much to appreciate about cottonwood trees. Each fluff is attached to a tiny seed and in much the same way as a dandelion, the fluff catches the wind to take the seeds far from the parent tree. Those fluff-borne seeds have an amazing ability to sprout in the hostile, ever-changing conditions of a stream bank.

Cottonwoods are scrappy survivors that grow up in rough and tumble river floodplain habitats. As a pioneer species, they are the first saplings to grow in the freshly deposited river sediments of floodplains. Their growth creates a more hospitable environment so that other plant-life can survive. This ultimately leads to a more stable stream bank and an ecosystem with greater diversity.

River floodplains are dynamic, constantly changing landscapes, which is why cottonwoods have adapted characteristics to survive becoming partially buried by river sediments. They have the ability to sprout new roots or branches from anywhere on the lower third of the trunk. They can also sprout roots from a broken branch that is carried to another spot.

Cottonwood trees grow quickly, up to five feet a year, and at heights of up to 100 feet, they are one of Minnesota’s tallest trees. They are also wide and sturdy trees. Their size and strength makes them important nesting sites for bald eagles, who like to build their enormous nests in trees that poke up above the tree canopy. The shade they provide protects other plants and animals in the floodplain, including fish and other aquatic species in the river.

The trunks, branches and leaves of cottonwoods provide food and shelter to many animals. They often become hollowed out, and that makes them a great place for squirrels, owls, woodpeckers and other cavity nesters. There are many species of butterflies and moths whose caterpillars eat cottonwood leaves, including the mourning cloak, tiger swallowtail and viceroy. Even our friendly neighborhood honeybees benefit from the sticky resin on spring leaf-buds, which they use to make “bee glue” (called propolis) to seal their hives. So, next time you see a giant tree with thick, deeply furrowed bark and triangular leaves, thank it for everything it does, fluff and all.

Learn more about Minnesota trees and learn to use a tree ID key during our Minnesota Trees Hike with a naturalist on June 9. Visit the Nature Center at North Mississippi (located at the east end of 49th Ave N. along the river) to check out a seasonal activity backpack to use while exploring the park. Come join in the fun at our Summer Kickoff Event on June 23, and play games, do a scavenger hunt, play with water, and face painting, too. If you have young children, come to our Nature Nuts playgroup for kids under six and an adult to explore the outdoors and learn about seasons, plants and animals.

June Public Programs: June 2—Early Birding: search for birds while on a naturalist-guided hike, 9-10:30 a.m.; June 9—Hike: Minnesota Trees: ID and learn more about our local trees, 1:30-2:30 p.m.; June 17—Family Funday Summer Arts and Animals: Meet animals and do art, 1-3 p.m.; June 23—Summer Kickoff Event, welcome summer with games, face painting and fun, 1-4 p.m.; and June 30—Nature Art Tie Dye, tie dye with a nature twist, Bandanna provided, $5, 2:30-3:30 p.m.

Sign up kids ages 6-12 for Summer Day Camps 8 a.m.-4 p.m. M-F $150 (full-day) or $80 (half-day). Camps run weekly, starting June 11 all summer long. Fee assistance is available – call for details.

Info/register for these programs at or call 612-370-4844. Do you have a question about nature in your own backyard? Then send it our way by emailing and it could appear in a future article. This month look for your favorite tree! Create a drawing or take a picture and think about what makes that tree special. Then show and tell a naturalist at the front desk to receive a North Mississippi Junior Naturalist button! Any images people would like to share will be displayed at the Center for the month of June. Like us on Facebook to stay in the loop about what is happening at your park!

This article was written by Victoria Thompson, Minneapolis Park & Recreation Board Naturalist at North Mississippi Regional Park