If trees could receive awards for being a United States all-star, surely the cottonwood tree would make the list. It has a long North American history and one can almost say it helped settle the West. From being large, stately shade trees to a source of food for humans and livestock, it has a long and important history.
Whether you inherited one in your landscape, are thinking of growing one or just want to learn about their long history, we cover all the important details. We also cover aspects of the tree’s care and growth.
Continue reading to learn all the important facts about cottonwoods. By the end, you’re sure to have a new appreciation for this fast-growing native.
Cottonwoods (Populus spp.) belong in the family Salicaceae, which is the same family as willows. They belong in the genus Populus, which is the same genus as poplar trees.
All types have a fast growth rate. When they mature, they have massive trunks and canopies that are around 100 feet tall and almost as wide. They can grow an additional 6 feet yearly. Due to this fast growth, their wood is considered weak, so they shouldn’t be planted close to structures. Their lifespan is relatively short, only living around 100 years.
There are three major types of cottonwoods: Eastern cottonwood (Populus deltoides), also called plains cottonwood or necklace poplar, Black cottonwood (Populus nigra), and Fremont’s cottonwood (Populus fremontii). Multiple hybrids also exist.
They are adaptable to a range of climate conditions but prefer sun and moisture. They are hardy within USDA hardiness zones 2 through 9. In the wild, they are typically found growing around the banks of streams, rivers, floodplain areas, prairie grasslands, as well as dry riverbeds. Due to this, the root system is shallow and seeks moisture, so the it shouldn’t be planted close to septic systems or waterlines.
They have broad trunks up to 6 feet across with deeply furrowed bark. Branches fill with flat, triangular-shaped, green, serrated leaves. Even with the slightest breeze, you can hear the leaves rustling in the wind. This is another identifiable characteristic of the tree. All species are deciduous. The green leaves change to a glorious color of yellow-gold in fall before dropping.
Trees are dioecious, which means springtime flowers are produced on both females and males. The male flowers pollinate trees with female flowers. Flowers are long catkins.
Its common name arrives from the cottony covering of the female seeds that ripen in summer. The cottony seeds can create a mess in the landscape. They blanket the area in white, as well as clogging air conditioners, window screens, and covering swimming pools. Due to this, many localities don’t allow female trees in residential areas.
To prevent this cottony nightmare, you can grow a male tree. Alternatively, the ‘Siouxland’ variety is a popular type that doesn’t produce seeds and only grows around 3 feet yearly.
History and Uses
Cottonwood trees are so beloved they are the state tree of Wyoming, Kansas, and Nebraska. Historically, the uses have been almost endless.
It was the only tree offering shade for those crossing the prairie grasslands. In fact, it was labeled “the pioneer of the prairie” due to its many uses.
Native Americans used the wood to make dugout canoes. They even showed Lewis and Clark how to make the canoes from the hollowed-out trunks so they could continue on their journey crossing the continent.
Because of its abundance and easy workability, early settlers used the wood to make barns and homes. Today the wood is still used to make shipping crates and pallets. The pulp is used in the manufacturing of paper products.
Saplings, twigs, immature branches, and bark were used for feeding horses. The inner bark was also used as a human food source. A bitter medicinal tea was also made from the inner bark.
Early settlers and Native Americans also used the trees as trail markers or meeting places.
General Care Guide
The two major considerations for caring for a cottonwood tree is their water and pruning needs. It doesn’t require fertilizer to produce good growth.
Another aspect of its care is fighting off a host of pest and disease problems affecting the tree.
Although trees are relatively drought-tolerant once established, regular moisture produces the best growth. Remember, these trees are found naturally growing along waterways or areas prone to floods, so they tolerate wetter conditions. For the best growth, water regularly, especially if it is newly planted.
Water newly planted trees several times weekly during the first season of growth. After that, irrigate weekly to every few weeks, especially if conditions are hot and dry.
Since the tree can quickly grow beyond your reach, it’s best to train it while it’s still young. Proper pruning develops a good structure and removes problematic branches. However, you should never top the canopy as you can weaken the tree’s overall structure. Carrying out light trimmings throughout the year is best instead of one major trim.
Cottonwoods develop stronger if they only have one main trunk. Prune off any additional suckers that develop at ground level. This job can be done year-round.
Since the wood is weak and prone to breaking, prune off any dead or damaged branches. You also want to prune off any crossing branches. As with the suckers, you can do this job year-round.
Of course, as it grows larger, you might need professional help when it comes to trimming.
Always use sterilized pruning tool blades when doing any trimming. This keeps you from unintentionally spreading an unwanted pest or disease to the tree.
Pest and Disease Care
Cottonwood trees are susceptible to a variety of pests and diseases. Quick action to control or prevent the problems is best. As with pruning, you may need a professional to come in and treat mature trees due to their huge size. Some problems are easily treatable, and some are not and can lead to the tree’s death.
Cytospora canker is generally the biggest threat. The fungal disease invades through areas of broken, weakened, or damaged wood. Since the spores are carried through rain, wind, and animals, it’s impossible not to have them make contact with the tree. The disease spreads through damaged portions and into the vascular system.
Once the disease enters the tree’s vascular system, it eventually dies. The best way to prevent the problem is by using sterilized pruning tools. Remove any weak, damaged or dead wood as you notice it.
Fungal Leaf Spots
Cottonwoods are susceptible to several types of leaf spots. As the name suggests, the problem rears its ugly head by showing up as spots on the foliage. Spots can be yellow or brown. Treatment can be a problem for mature trees due to their size. However, you can help prevent the problems by keeping the area clean.
Use a fungicide like mancozeb, chlorothalonil, or cupric sulfate to prevent new problems. Fungicides won’t cure already affected foliage.
Prevent future problems by watering early in the day, allowing the tree good air circulation and cleaning up fallen leaves and debris.
Cottonwood Leaf Beetle
The cottonwood leaf beetle’s major damage is defoliating the tree. In most cases, trees can survive the attack and only lose their good looks. However, in severe infestations where defoliation is more than 40 percent, trees can die. Identifying and treating the pest problem in its early stages of development usually prevents serious outbreaks.
Beetles are around 1/4 inch long. They are black with yellow wings with black stripes. The pest overwinters in fallen debris or crevices in the bark. In spring, the beetles mate and begin feasting on the foliage. Females then lay clusters of eggs on the underside of leaves.
The 1/2 inch long, black larva feeds on the underside of the foliage. In about two weeks, the larva pupates. In around 510 days, adult beetles emerge and repeat the cycle.
If an outbreak isn’t severe, you don’t have to do anything. However, if it’s starting to lose a lot of foliage, treatment is advised. You can use insecticidal soap, horticultural oil, or neem oil to treat and control the larva. If treating the beetle, use a product containing carbaryl, diazinon, or acephate.
Site Selection and Growing Tips
Growing cottonwood trees in an ideal location is the first step in promoting good health. Due to its potential size, a proper site is important to its longevity. It also reduces potential problems with pests and diseases. Consider its mature size, weak wood, and invasive root system when choosing a permanent location.
Preferred Soil and Light
For proper growth, cottonwood trees require a location situated in full sun. They tolerate growing in average soils that are well-drained, wet to moderately wet. This makes them suitable choices to grow next to water features, rivers, streams, or ponds. Although relatively drought-tolerant once established, regular water applications produce the best growth.
When selecting an appropriate site, remember this grows into a humongous tree. It will definitely bring shade to any area where it resides. It’s also useful as a windbreak.
Select a permanent location where the cottonwood can achieve its mature size without interference. You don’t want to plant it close to structures or powerlines. Since the wood is weak, make sure to consider the possibility of branches falling and causing damage to nearby structures.
To reduce possible disease and pest problems, it requires adequate space to grow and receive good air circulation.
Since the root system will seek water, don’t plant it close to a septic system or water lines. The roots can damage the pipes as they attempt to gain water.
Keep an area of around 3 feet in diameter free of unwanted growth under the tree. This prevents the bark on the trunk from being injured by lawn equipment bumping into it. Damage to the bark opens the tree up to possible problems with disease and pests.