Cottonwood Trees in Denver: Should You Remove, Treat, or Keep?

Cottonwoods are native to Colorado’s Eastern Plains. They grow in wetter soils along rivers, lakes, and irrigation ditches in groves or bosques. Caring for Cottonwoods in urban landscapes requires significant space, consistent watering, and proactive pruning to manage their rapid growth. No tree divides Denver homeowners quite like the Cottonwood. The trees grow large, and in spring they provide ample shade. By early summer, they blanket yards, patios, and pools in cotton. Later in the season, their roots sprout in neighbors’ yards, causing a nuisance. On top of that, a mature tree will consume hundreds of gallons of water on a hot summer day. For many homeowners, the question becomes inevitable: keep the tree, manage it, or remove it altogether?

Cottonwoods Seen As Valuable

The answer is not simple, because Cottonwoods are both valuable and problematic. They were widely planted across Denver during the post-war housing boom because they provide shade so quickly. Cottonwoods can grow four to six feet per year, creating a full canopy in less than a decade. In the 1990s, forester offices stopped recommending Cottonwoods for several reasons. First, they become enormous. It is not usual for a mature tree to stretch across several yards, dwarfing the homes below. Next, they are relatively short-lived. Red Oaks can live 200 to 400 years, while in urban settings, Cottonwoods start to fail after 30 to 50 years. Some live to 100, but it is rare.

Driving through some of Denver’s older neighborhoods, such as Hilltop, County Club, and Washington Park, many homeowners with large yards choose to keep their trees—and for good reason. Large Cottonwoods make a statement in mature landscapes. They provide a level of shade that is difficult to replace. For homeowners who choose to keep their Cottonwoods, proactive pruning is a must. Regular structural pruning every few years removes damaged branches and deadwood. Opening the crown lets in more sunlight, promoting healthy growth and preventing fungal infections. Proactive pruning involves a certified arborist inspecting trees to monitor changes over time and address issues before they become serious. This level of care represents an ongoing investment, but it is often necessary to safely maintain a large Cottonwood in a residential setting.

Are Cottonwood Trees Dangerous?

Cottonwoods are viewed as dangerous or problematic because they are short-lived, fast-growing trees with softer, more brittle wood and trash-tree characteristics. These trees are also susceptible to fungal diseases and insects. Keeping Cottonwoods properly watered and pruned helps the trees’ natural defenses fend off these ailments and pests. Cottonwoods have the following issues.

Branch Dropping: Unlike slower-growing species, mature Cottonwoods are known for dropping large limbs during windstorms or without warning. What does a person do when their tree drops a large branch, damaging their neighbor’s Tuff Shed? They make sure they have good liability insurance.

Aggressive Root Systems: Cottonwoods are always thirsty, so their roots aggressively seek water, invading sewer lines and lifting sidewalks and driveways. Their roots can also damage building foundations.

Structural Weakness: Walking along the river bottomlands in Eastern Colorado shows that Cottonwoods are weak trees. It looks like a war zone with large branches and trunks lying on the ground and stacked up willy-nilly.  As these trees age, they often show signs of decline, including thinning canopies, deadwood, hollowness, or structural weakness. These short-lived trees, planted in small lots in urban neighborhoods, will become problematic. When to remove a Cottonwood becomes a topic of discussion with the property owner and their neighbors.

Cytospora Cankers: Cottonwoods affected by drought, polar plunges, insects, sunscald, and root damage are susceptible to Cytospora. Cankers on stems and branches are often elongated, slightly sunken, and discolored areas in the bark. The disease can grow fast on highly stressed trees. The best treatment is prevention.

Cottonwood Borer: The Longhorn borer is one of the largest beetles found in North America. The female chews small pits at the base of the tree to lay her eggs. Young Cottonwoods are more susceptible to the larvae of this insect. Adults feed on leaf stems.

Popular Borer: The larvae of these borers tunnel through the sapwood, causing structural weakness. Large infestations can kill trees, so treatment is recommended.

1. Upper Canopy Thinning
   
   

   
   Look at the top branches, if they are bare or are slow to leaf out during the growing season.

2. Excessive sucker growth
   
   

   
   New shoots sprouting from the base of the trunk indicate stress.

3. Cankers and oozing sap
   
   

   
   Look for Cytospora cankers on the branches or trunk.

4. Cracks in the trunk or major limbs
   
   

   
   Vertical splits or weak branch unions signal structural risk.

5. Fungal growth
   
   

   
   Mushrooms or conks at the base of the tree can indicate internal decay.

6. Insect activity
   
   

   
   Evidence of borers (like cottonwood or poplar borers), including holes, sawdust-like frass, or bark damage.

7. Premature leaf drop or discoloration
   
   

   
   Leaves turning yellow or dropping early in the season.

8. Dead or dying limbs
   
   

   
   Large branches without leaves during the growing season are a major red flag. Probably time for removal.

9. Leaning and ground movement
   
   

   
   A noticeable shift in the tree’s position or soil heaving around the base. Immediate hazard.

10. History of limb failure
    
    

    
    If the tree has already dropped large limbs, it often points to systemic decline. Immediate hazard.