Questions are coming into OSU Extension offices about clumps of white, cottony, fluff wafting through Ohio’s forests and landscapes. The culprits behind the fibrous phenomenon are female eastern cottonwood trees (Populus deltoides, family Salicaceae).
Cottonwood trees are dioecious, which means there are male and female trees. The name is derived from the Ancient Greek meaning “two houses.” Ginkgo (Ginkgo biloba) trees are another example, with only the females producing the odoriferous fruit-like seed structures. Wafting butyric acid fumes are far worse than wafting cottonwood fluff.
Monoecious means “one house,” with the same tree having male and female reproductive organs. Oaks (Quercus spp.) are a good example.
Cottonwood Confidential
Cottonwood reproduction starts with small male and female flowers forming on short, pendulous stems hanging from twigs; a flower arrangement called a catkin. Pollen from the catkins on male cottonwood trees drifts on the wind to pollinate female flowers in early spring.
Once pollinated, the female flowers develop into strands of small, green seed pods, also called seed capsules. The seed capsules look like a string of beads.
At maturity, the capsules split open to release seeds attached to white, cottony fluff, which gives the cottonwood its common name. On stiff winds, the airy fluff can waft the seed considerable distances. On still winds, the fluff descends to litter the ground beneath the trees.
Seed production appears to be unusually heavy this year in southern Ohio. There’s a chance that the cotton-wave will progress northward to produce fluff tsunamis where cottonwoods rule along Lake Erie.
Cottonwood Consternation
The cottonwood seed fiber may occasionally present a diagnostic challenge. Clumps of white fluff hanging on plant stems, sticking to leaves, or appearing in other unexpected places may evoke scenes from Stranger Things.
Shifting winds can blow cottonwood fluff to locations where it was not a common sight in the past. Ohio landowners may remark that their cottonwood trees never produced the seed fluff before. It’s important to ask about the age of the tree because it takes several years for female cottonwood trees to mature to produce seed.
Cottonwood fluff from the female trees is usually a short-lived nuisance. However, massive quantities of the fluff may clog air conditioners, car radiators, and swimming pool filters. Also, the delicate fiber is highly flammable, so it can be hazardous around open flames. The whimsical fluff can be equal parts magic and misery.
Eastern cottonwood trees can also present a safety challenge. The species dedicates energy to fast growth and reproduction at the expense of producing strong wood. Big cottonwoods are notorious for dropping large branches. The trees should not be planted near structures.
Criminal Cottonwoods
Some U.S. cities have ordinances banning planting Eastern cottonwoods. Oklahoma City’s Code of Ordinances, 53-5, titled Certain Trees Prohibited reads: “No person shall plant or permit the planting of black locust, seed-bearing female cottonwood … The male non-seed-bearing cottonwood tree is specifically excepted from the provisions of this section.”
The Sidney (OH) Code of Ordinances, Section 905.13, titled, Cottonwood Trees Prohibited, reads: “No person shall plant, or cause to be planted, trees of the cottonwood variety within the City.” Interestingly, Sidney also has an ordinance against tree topping (Section 905.10). That’s an ordinance we can all get behind!
Another common concern with cottonwoods is whether the cottony material contributes to nasal allergies. I could find no evidence that cottonwood fluff triggers allergic reactions. If people are suffering from hay fever during the release of cottonwood fluff, the source would be another allergen, such as wind-borne pollen from grass, weeds, and other trees.
However, while cottonwood fluff is nothing to sneeze at, the male pollen is a different matter. Mature trees can release large quantities of pollen from the male flowers. Albuquerque, NM, includes cottonwoods in a list of banned trees on its website titled, “Restricted Trees for Pollen Control.”
The Soft-Side of Cottonwoods
I’ve long admired our native eastern cottonwoods … at a distance. Mature trees can be huge, growing more than 80’ tall with a canopy spread greater than 60’. They can rival neighboring American sycamores (Platanus occidentalis) growing in shared riparian habitat. The shade provided by the fast-growing trees with huge, spreading branches is appreciated by anglers and picnickers.
Cottonwoods transition from white, smooth bark on young trees to thick, dark, deeply fissured bark on mature trees. Like other members of the genus Populus, their triangular leaves flicker in the wind, creating a shimmering effect accompanied by a subtle rustling.
Eastern cottonwoods are tough trees that are tolerant of drought and a wide range of soil pH. They commonly grow around lakes and streams, where their strong root systems play an important role in holding back erosion. They have great wildlife value and provide many environmental services that make them important members of forest and riparian ecosystems.
Although eastern cottonwoods grow fast, they can be surprisingly long-lived. I took the picture below in 2008 of a large cottonwood tree in Ripley, OH. I don’t know if the tree still exists, but sadly, an online “visit” using Google Maps showed the tree was in a significant state of decline in 2024.
During my 2008 visit, I found a marker beneath the tree designating it as a “Witness Tree.” The marker read, “Growing on the Ohio Riverbank for more than a century as a witness to river history and many seasons of change.” Even if the tree no longer exists, it certainly lived a long, eventful life.
Our native eastern cottonwoods can be planted and enjoyed in parks away from locations where their misbehavior presents a challenge. They are tough trees. The image below shows a cottonwood planted in a park in Butler County, OH. I’ve long admired the tree and have watched it rapidly produce a large crown providing shade along the walking path.
The cotton problem can be solved by selecting “cottonless” cottonwoods, such as the cultivars ‘Siouxland’ and ‘Sparks,’ as well as the hybrid Populus x canadensis ‘Robusta.’ These selections also have other valuable growth qualities not found in the straight species.
