Denver is home to a myriad of cottonwood trees.
Cottonwood trees are as much a staple of life in Denver as the Broncos, the Platte, and shoveling out of a spring snowstorm. Cottonwood trees are known for their massive trunks, rising canopies to well over 50 feet, even 60 feet in many cases, and releasing their telltale ‘cotton’ in the form of fruit from female cottonwoods.
Early to mid-June is when cottonwoods tend to release their ‘cotton’, making lawns from Aurora to Longmont, Lakewood, and everywhere in between look like a light snow fell. This seasonal release can also be a literal headache for those with allergies. If you have any level of seasonal allergy, you’re probably well aware when the cottonwoods are ‘in season’.
Cottonwood trees are massive and beautiful to behold. They are known for their stately presence and more than a few families in Denver have fond memories of tire swings, tree forts, and summer days spent in the shade of cottonwoods.
Whether you’re new to Denver or a Colorado native with cottonwoods on your property, there are several questions you may have about taking care of your cottonwood trees:
- What’s the best way to trim a cottonwood tree?
- What are some of the biggest threats to my cottonwood tree?
- Will a cottonwood tree take over my property?
- How do I safely and quickly remove a dead cottonwood tree?
Our team at Fielding Tree & Shrub Care know what it takes to protect, treat, and take care of cottonwood trees in a way that maximizes the tree’s longevity and protects your property. In this article, we want to share ‘all things cottonwoods’ with you so you have the information you need to make your cottonwoods thrive, not just survive in Denver.
Cottonwood Trees 101
The first thing you may want to know is there are two main species of cottonwood trees in the Denver metro area: narrowleaf cottonwoods, and plains cottonwoods. Here’s some amazing information from our friends at the Colorado State Forest Service about each of these amazing species:
Narrowleaf Cottonwood Trees (populus augustufolia)
- Bark: Yellow-green and smooth on young trees; thick, gray-brown and furrowed with interlacing ridges at maturity.
- Leaves: Broad-leaf foliage is shiny green with a pale underside; narrow and 2 to 3 inches long; lance shaped with a fine, serrated edge and a pointed tip.
- Fruit: Light brown, hairless fruit; inch long; many broad, egg-shaped capsules that mature in the spring, then split into two parts containing many cotton-like seeds.
- Elevation: 5,000 to 8,000 feet.
- Height: Up to 60 feet.
- Habitat: Moist soils along streams; can often be found with willows and alders in coniferous forests.
- Relation to Fire: Severe fires can easily kill both young and mature trees. Young trees are able to sprout from roots and/or branches after a fire. (Colorado State Forest Service)
Plains Cottonwood Trees (populus deltoides)
- Bark: Green-yellow and smooth while young; dark gray, thick, rough and deeply furrowed at maturity.
- Leaves: Broad-leafed foliage is glossy and yellow-green; 3 to 6 inches long, 4 to 6 inches wide; toothed margins.
- Fruit: Inch long with capsules containing 3 to 4 valves; many tiny, cotton-like seeds inside valves.
- Elevation: 3,500 to 6,500 feet.
- Height: 36 to 190 feet.
- Habitat: Found in floodplains, bordering streams, near springs and in moist woodlands; pure stands or with willows.
- Relation to Fire: Generally killed by fire; very poor sprouting response. (Colorado State Forest Service)
Of the two species, narrowleaf cottonwoods and plains cottonwoods, there tend to be more narrowleaf cottonwoods in the Denver metro area. Whatever species may be occupying your property, you may be noticing your cottonwood looking a bit sickly. It’s because cottonwoods tend to have a lifespan of about 30 years, which is consistent with when much of the housing boom happened in the mid-80s to early-90s across the Denver metro area.
At the time cottonwood trees were not yet illegal to plant (more on that later), and they were a popular choice for developers to populate new properties because of their rapid growth rate. Now that we’re approximately 30 years after the housing explosion in Denver, those same cottonwoods are posing massive problems for property owners.
Are Cottonwood Trees Illegal to Plant In Denver?
This may surprise you, but cottonwoods have been outlawed in much of the Denver metro area for the greater part of the past ten years. So, why is it illegal to plant cottonwoods in Denver? Because they are a massive and invasive tree species, and they have a habit of wanting to share your living space and even your utilities.
Cottonwoods are part of the populus tree species, the same species family as aspens. If you’re familiar at all with aspens, then you know that an entire mountainside of aspens may, in fact, be only one tree that branched out, sprouted up, and continued growing. It’s because aspens and cottonwoods are highly invasive in their surrounding areas. While some trees have a taproot (one main root that grows straight down), cottonwoods and aspens grow a wide range of roots that have a voracious appetite for water.
This all sounds well and good until someone plants a cottonwood tree in a front yard less than 20 feet away from the main water supply. Within a matter of years, a normal cottonwood will quickly find and break into the water supply ductwork. This means massive cleanup on the behalf of the homeowner, not to mention the financial cost of repairs and the hassle of a messy front yard.
And, it can get worse, because it’s not just incoming water sources that cottonwoods love. They search for any ‘liquid’, water-type source, so your outgoing sewer line is often just as easily the victim of thirsty cottonwoods. That’s when you end up in deep ‘stuff’, as well as having the same type of problem as before but with a horrible smell.
Cottonwoods also have incredibly strong root systems, which serves them well for longevity and poses another threat to homeowners. Cottonwoods planted to close to structures, namely basement walls and garage foundations, will break through the concrete walls over time. You may love having a big basement, but no basement is meant to have a cottonwood as a live-in guest.
This is why cottonwood trees are largely illegal to plant in the Denver metro area. Homeowners, HOAs, city officials, and repair crews are tired of cleaning up after cottonwoods. However, if you have a significant amount of property, you may still consider planting a cottonwood. We highly recommend checking with your local forestry service, HOA, and/or city authorities to see if cottonwoods are permissible for new plants.
What’s the Cotton from Cottonwood Trees?
Fun fact: cottonwood trees are also dioecious, which means they have male and female flowers on different trees. Male cottonwood trees (“cotton-less”) are not capable of producing the cotton, which is why many neighborhoods that do allow new cottonwood trees restrict planting to only male cottonwood trees.
Female cottonwood trees (“cotton-producing”) are pollinated by male cottonwood trees in early spring and they then produce small capsules. These capsules contain small seeds that are carried through the wind because of the ‘cotton’ found in the capsules. For allergy sufferers, it’s the male cottonwood trees that are often the cause of heightened allergies in early spring.
It can take a cottonwood seedling many years to fully develop and start producing pollen or pods, depending on whether the tree is male or female. Many of the cottonwood trees in Denver have reached their full maturity and will stop producing as their life-cycle comes to a close.
Common Threats to Cottonwood Trees In Denver
Cottonwood trees are more than a little cranky about cankers, specifically cytospora canker. The cytospora canker poses the greatest invasive threat to cottonwood trees, which already have weaker wood density than many trees. Cytospora canker is a fungal disease that invades cottonwood trees through damaged and weakened woods. The deadly spores are carried by animals, wind, and rain, which makes it virtually impossible to prevent cytospora canker from contacting cottonwood trees. Over time the infection spreads through the main vascular and skeletal structure of the cottonwood, which leads to eventual death.
One of the best defenses against cytospora canker in cottonwoods is to remove any diseased, dying, or dead wood at the first opportunity. This is not an easy nor safe process without the proper equipment and care. We highly recommend you contact our team at Fielding Tree & Shrub Care if you have a cottonwood tree suffering from cytospora canker.
Trimming and Maintenance Tips for Cottonwood Trees
Cottonwood trees grow at a rapid pace, as much as six feet per year for new seedlings. With Colorado’s heavy spring snows and high winds, cottonwood trees can be susceptible to breakage. As a rule of thumb, never ‘top’ your cottonwood tree. This practice is extremely harmful to your tree’s overall health and it doesn’t provide any specific benefit to the branches below. In fact, topping your tree may create a maligned canopy that doesn’t allow your cottonwood tree to grow as designed.
Cottonwood trees are heavy and can be dangerous if neglected at all, which is why we want to share this information with you. Taking care of cottonwood trees in Denver is what we do best. Our Fielding Tree & Shrub Care team loves seeing big, beautiful cottonwoods thrive and get the care they need.
Whether your cottonwood needs a little ‘haircut’ or even if it’s died and needs proper disposal, we will treat your tree and your property with the utmost respect. That’s why we’re Denver’s favorite arborist. Schedule your complimentary on-site inspection of your cottonwood tree today.