Cottonwoods are poplars native to North America, Europe, and western Asia. They usually occupy wet riparian areas in the East or seasonally dry creek beds in the West.
The name comes from the fluffy white cottonlike covering that appears when the female trees produce seeds. There are three varieties of cottonwood that grow in the United States and Canada:
Eastern cottonwood (Populus deltoides), found in the eastern U.S. and southeastern Canada, including Ontario, Quebec, North Dakota, and Texas.
Black cottonwood (Populus balsamifera), found west of the Rocky Mountains. It grows as far north as Kodiak Island, Alaska, and as far south as northern Baja California.
Fremont cottonwood (Populus fremontii), found in California growing east to Utah and Arizona and down into northwest Mexico.
Cottonwoods are very similar to—and share a genus with—other true poplars and aspens. That genus is called Populus, and all “members of this group of trees may be called cottonwoods, poplars, or aspens, depending on what species they are.”
These trees like wet conditions and can even tolerate areas that see temporary flooding. Historically, their presence was used as an indicator for water. When they are not surrounded by other trees or buildings, they are often spread out as wide as they are tall. They are extremely intolerant of shade, requiring as much full sun as possible to grow and thrive. They are said to be one of the most shade-intolerant hardwood tree species, second to only black willow
Cottonwoods are among the tallest and fastest growing hardwoods in North America, adding up to seven feet in height every year and attaining overall heights of over 150 feet. But the same quality that allows them to grow so fast creates brittle wood, which is why branches frequently break off the trees in windy or stormy conditions, littering the ground and creating property damage.
The wood from these trees is commonly used to make storage boxes, crates, paper, matchsticks, and plywood. It is easy to carve, making it popular with artisans as well. Herbalists sometimes use the buds and bark of cottonwood to treat aches and pains and skin irritations.
Identifying the Different Cottonwoods
The three cottonwood subspecies found in the U.S. and Canada are similar in some ways—such as their tendency to grow tall—and different in others, like leaf color and growing conditions. In general, cottonwood leaves are alternate and triangular, growing on flattened leafstalks. Their bark is yellowish-green and smooth on young trees but grayish-brown and deeply furrowed with scaly ridges in maturity.
Branches are usually thick and long, and foliage is uneven. Cottonwoods typically produce catkin flowers, though they vary in color.
There are separate male and female cottonwoods (known as a “dioecious” species), but only the females produce the flowers with the fluffy white “cotton” that helps to disperse the seeds further afield. So if you’re worried about that cotton clogging screens or AC filters, you could just plant a male cottonwood instead.
Here’s how to distinguish between the different subspecies.
Eastern Cottonwood
The eastern cottonwood (Populus deltoides) is among the top 100 most common trees in North America. It’s also one of the largest hardwood trees on the continent, even though the wood is rather soft (as well as brittle). It’s a riparian tree, meaning it grows along the banks of waterways and along the edges of floodplains. It occurs throughout the eastern U.S., as far north as southern Canada.
Males produce reddish catkins, while females produce yellowish-green catkins. Both males and females produce green capsule-looking fruits, but only the females make cotton, while the males make pollen. In some locales, the male trees are banned due to human allergy concerns linked to the pollen.
Some of the trees have multi-stemmed trunks. The leaf stalk is nearly as long as the leaf itself, which causes it to droop off the branch. The stalk flattens where it meets the leaf blade, and there are usually several warty glands at the point where it joins. The fairly long leaf has a straight or heart-shaped base, large rounded teeth along the edges, and a pointy tip.
Black Cottonwood
The black cottonwood (Populus balsamifera), also called the Western balsam poplar or California poplar, grows mostly west of the Rocky Mountains and is the largest cottonwood in the west. It is distinguished by its leaves, which have fine teeth unlike those of other cottonwoods. Black cottonwood leaves may also have an ovate shape, and the leaves on mature trees may show a light rust color or blotches of brown on the side facing the ground. They are dark, shiny green, two to five inches in length. The tip is always sharply pointed.
In terms of flowers, these cottonwoods produce yellow catkins on both male and female trees. The fruits of black cottonwoods are similar to those of the eastern cottonwood except that they have a hairy appearance. The branches may have buds that are sticky with resin and fragrant. The bark of older trees is deeply furrowed.
Fremont Cottonwood
The Fremont cottonwood (Populus fremontii), also known as the western cottonwood or the Rio Grande cottonwood, occurs in California east to Utah and Arizona and south into northwest Mexico. Named after 19th-century American explorer John C. Fremont, it is similar to the eastern cottonwood, differing mainly in the leaves having fewer, larger serrations on the leaf edge and in the flower and seed pod structure. Leaves are triangular or heart-shaped, and light green with white veins, turning golden yellow in the fall.
The Fremont cottonwood’s fruit differs from other subspecies’ in that it is light-brown and egg-shaped. It bursts into three to four sections to release its seeds. Both genders produce red catkins.
