Native to the United States, cottonwood tree's preferred habitat in the wild include moist bottomland areas and around lakes and streams. People who want to add one to their landscape need to consider all aspects of the tree before planting as the tree has a variety of drawbacks that don't make it suitable for many locations.
Classic Cottonwood Looks
Cottonwood (Populus deltoids), commonly called eastern cottonwood, is a fast-growing deciduous tree that obtains an additional 6-feet of growth yearly and reaches a mature height and width of 100 feet. Due to this habit of quick growth, the wood is soft and brittle, breaking easily in windy conditions.
Bark, Stems, and Foliage
The bark and trunk of a mature tree is deeply furrowed, thick and gray. The bark is a greenish-gray on younger trees. Young stems and branches are a yellowish-green in color, changing to a grayish color as they age. Mature trees develop an open and irregular-shaped crown.
Foliage is thick and heart-shaped with coarse ridges lining the edges, averaging 2 to 6 inches long. During the growing season their color is green, changing to yellow during the fall before the foliage drops during the winter months. The several inches long, flattened petiole allow the leaves to flap from side to side in windy conditions.
Flowers and Seeds
Eastern cottonwood trees are dioecious, meaning there are male and female trees producing flowers, though the female trees are the ones producing the cotton-like substance giving the tree its name. Trees start producing seeds when they get around 10 years old.
Before the foliage sprouts in springtime, 6-inch reddish-yellow catkins hang from the branches and develop into seeds. Each rounded seedpod contained on the mature catkin hold multiple seeds, with female trees producing seeds surrounded by a cotton-like substance. Seedlings easily sprout and it's not unusual to find them sprouting under the tree's canopy and surrounding areas where they fall.
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Drawbacks and Landscape Considerations
Due to the tree's large size and tendency for breaking limbs, it requires a sizeable area in the landscape to achieve its mature size out of the way from structures or electrical wires. Cottonwood trees make good shade trees when planted in the appropriate location.
When considering a permanent place for the tree, consider its aggressive root system that seeks out moisture. Do not plant near septic systems as the roots will seek it out and can damage the system creating an expensive repair. You also don't want to plant the tree close to the home's foundation or a sidewalk as the roots can lift the area and cause damage.
Female tree's seeds create a cottony mess over yards. The seed dispersal is so extensive they can cover the area like a blanket of snow. In fact, the seedy mess is so bad that some locales don't permit the planting of female trees along sidewalks or walkways. To prevent this from happening gardeners should plant a male cottonwood that doesn't produce the cotton such as the male cultivar "Siouxland."
Buying Considerations
Since the trees grow so fast, you are most likely to find 1-year-old trees and younger in local nurseries throughout its growing range. Online nurseries ship trees while in their dormant stage and barerooted. Sizes typically range from 1 foot to 4 feet tall. Some online nurseries selling cottonwood trees are Nature Hills and Porcupine Hollow Farms - be sure to check back or sign up for stock notices if they are out of stock as it may not be the right season for shipping.
If purchasing a tree at your local nursery look for healthy trees that have good leaf color and show no signs of pests or disease problems. Check the container to make sure the roots are not growing out of the bottom, meaning the root system has outgrown its pot. Trees with wrapping root systems sometimes never grow properly once planted into the ground.
Preferred Growing Conditions
Cottonwood trees are hardy trees and aren't too fussy about their growing conditions, so even black-thumb gardeners should have success growing one. They have a wide hardiness range, growing well in USDA zones 2 through 9, so they do well in almost all regions throughout the United States.
Preferred Light
The tree tolerates partial sun, but puts on its best growth situated in a site receiving full sun.
Preferred Soil
Cottonwood trees grow in a wide range of soil types and puts on its best growth in those with a tendency to be moist. However, it does not tolerate growing in soil that is constantly soggy and wet.
Basic Requirements for Care
Since the trees grow so quickly and aren't fussy about their growing conditions for healthy growth, the main requirements for care are providing enough moisture and pruning. The tree doesn't require fertilizer applications for healthy growth.
Moisture Requirements
Cottonwood trees are relatively drought-tolerant once established, but while the tree is young or newly planted, gardeners should apply weekly applications of water. However, the tree performs best with regular water applications.
Pruning Requirements
Since the tree grows so tall and wide, once the tree reaches its mature height and width, it's almost impossible to do extensive pruning to the tree without the assistance of a trained arborist. When the tree is young, though, it's important to prune so the tree develops a strong structure.
Prune off any water suckers that develop around the trunk so the tree only has one main trunk. Trim off any dead, damaged, or diseased limbs anytime throughout the year. You will also want to remove any crossing branches or those that might interfere with a structure. Always make sure you sterilize your pruning tool blades so you don't transfer any disease or pests to the tree.
Pest and Disease Problems
Another drawback to these trees is they are prone to a multitude of diseases and pests. These problems can shorten the life of the tree and due to its enormous size; problems can be hard to treat.
Common Pests
The two most common pests infesting cottonwood trees are the poplar petiole gall aphid and cottonwood leaf beetle, which is the more destructive of the two. Most of the time pest problems are preventable by cleaning up fallen debris around the tree.
- Poplar petiole gall aphid: Cottonwood trees infested with gall aphids show signs by small bumps forming along the leaf stems. The bumps contain the overwintering aphids who split open the gall in springtime and release winged adult aphids. The aphids do not damage the tree, other than producing unsightly galls, and control isn't required.
- Cottonwood leaf beetle: Cottonwood leaf beetles are serious and quick defoliators, especially of trees 3 years old and younger. If you notice a small beetle with a black head and yellow and orange markings on its body, it's likely a problem for you. The beetle overwinters in fallen leaf debris or under the tree's bark and emerges in warm temperatures to feed on the tree's foliage eventually skeletonizing it, which can be detrimental to the tree's growth. When outbreaks aren't severe, predatory insects kill the pests, but when outbreaks are severe, gardeners may have to treat the entire tree with the insecticide's Neem oil or Bacillus thuringiensis. If dealing with a large mature tree, you may have to call in a professional to reach all areas of the tree when treating it with an insecticide.
Common Disease Problems
Gardeners adding a cottonwood tree into their landscape will more than likely face an eventual problem with the tree, as they are prone to many disease-related problems. Some of the problems do not warrant control as the situation isn't life-threatening, while other problems are treatable by keeping the area underneath the tree clear of fallen debris.
Many problems enter the tree through wounds, which generally happen due to injuries from lawn equipment. Therefore, it's important to keep the area underneath the tree's canopy free of weed and grass so there's no need to use a mower or weed trimmer around the tree's trunk. Some of the common diseases affecting these trees are:
- Cytospora and septoria canker fungus: These fungal problems are hard to distinguish from each other and affect unhealthy trees by using unsterilized pruning tools or wounding portions of the bark makes trees more susceptible to the disease. The problem shows as cankered areas on stems and branches, which eventually look watersoaked and brownish-red. The only control is pruning off affected portions of the tree, making sure to cut the entire diseased section from the tree and into healthy wood. When severe, the fungus can eventually kill the tree.
- Heart rot fungus: Wounding the tree's trunk allows the fungus to enter the tree which affects its heart and the tree eventually rots and dies. Signs of the problem appear as conks attaching to the tree's trunk, generally at the base and there is no treatment. Prevent the problem by not wounding the tree's trunk and bark.
- Fungal leaf spots: Cottonwood trees are susceptible to various types of fungal leaf spots that appear as discolored areas on the tree's foliage. Depending on the specific fungal problems, the spots appear as grayish or brownish and if left untreated, defoliation occurs. Control the problem as soon as you notice an outbreak using a copper fungicide and spraying the entire tree once each month.
- Fungal rust spots: Fungal rust spots appear on the foliage, generally a rusty or yellowish color, which turn darker over time. The problem is most severe during winter, isn't life-threatening to the tree, and warrants no control, as the problem is only cosmetic.
- Powdery mildew fungus: Powdery mildew is one of the easiest identifiable problems associated with the trees, and as its name suggests, a white powdery coating covers the foliage. The fungus is most problematic when nights are cool, but humidity is high. The problem is generally cosmetic and doesn't warrant control, but in the event of a severe outbreak, spraying the entire tree with a copper fungicide and reapplying every four weeks should control the problem.
- Phymatotrichum root rot: This is a fungal problem affecting the soil which transfers to the tree's root system and there isn't any control options for the tree. The condition is most severe during summer and gardeners may notice the foliage quickly turning bronze and wilting within days, but remaining attached to the tree. The only option is removing the tree from the landscape.
An Attractive but Problematic Tree
Cottonwood trees aren't as utilized in landscapes as they once were due to all the problems associated with them. However, if planted in the appropriate location where the soft wood and aggressive roots don't cause damage, they make attractive quick-growing shade trees, especially male cultivars.
