At a Glance
Height: 40-60 feet
Spread: 30-40 feet
Shape: Narrow, upright, pyramidal
Exposure: Full sun
Leaves: 2-4 inches long, 1-2 inches wide, oval with a pointed tip. Green on top, dull green underneath. Shaped like the head of a spear, hence its name
Fruit: Catkins 4-5 inches long – no seed
Drought-tolerant? No. High water requirement
Bark: Light gray-brown
Where to Plant: Water regularly but do not overwater. Requires constantly moist soil. Needs full sun. As with the other cottonwoods, do not plant too close to buildings because of the invasive root systems. Can tolerate a variety of soil types.
Common Problems & Possible Causes
Cracked, dying bark or oozing white foam – Slime Flux
Yellow spots and sticky residue on leaves – Aphids
Cracked cankers, discolored bark or oozing resin – Cytospora canker
Honeydew excretion, incredibly small insects on the underside of leaves – Scale insects
About All Cottonwood Trees
Cottonwood trees are a common street tree and are the largest native broadleaf trees in Colorado. Their wide-spreading roots are helpful in reducing erosion and slowing floodwater runoff. They are also a popular habitat for various forms of local wildlife.
Cottonwoods get their name from the white fluff that floats off the trees; these resemble cotton and contain the tree’s seeds.
Due to the snow-like seeds, brittle branches that break easily, and suckers that pop up everywhere, many cottonwoods are considered “messy” trees.
Though some cottonwood trees can live over 100 years, many in urban areas only have a lifespan of around 30 years.
Many communities in the Denver metro area have banned the planting of cottonwood trees because of their large size and invasive root systems. On smaller properties, they just don’t have enough room to grow. Their roots are strong and can break into plumbing lines (especially if there already is a crack) and can contribute to damaging the foundations of buildings.
Neighborhoods that do allow cottonwood trees to be planted often insist on planting only male trees, as they do not produce seeds (and, therefore, no messy cotton fluffs). However, male cottonwood trees are often the ones that negatively impact allergy sufferers the most.
Because cottonwood trees are extremely fast growers (some varieties can grow 6 feet a year), the wood is more brittle than other types of trees. With heavy snowfall, this can contribute to significant branch and limb breakage on cottonwood trees. Proper pruning can help to eliminate any broken or dead branches, but cottonwood trees (like all trees) should never be topped.
Cottonwood trees are not particularly fire-resistant, but their roots are important in keeping soil together to reduce runoff and slowing floodwater. The Colorado State Forest Service has produced this document that has recommendations on how to reduce wildfire risk in cottonwood groves.
About Lanceleaf Cottonwood
Lanceleaf cottonwood, occasionally called lanceleaf poplar, is actually a naturally occurring hybrid of narrowleaf cottonwood and plains cottonwood. As you’d expect, it is found where the ranges for those two cottonwoods overlap. Native to the Rocky Mountains, the it grows primarily at elevations between 4,500 and 8,500 feet.
It is an especially fast-growing tree that needs lots of sun and water to supplement its rapid growth. It can add shade quickly and develops a beautiful pyramidal form. Although it’s shorter than the other cottonwood trees found in Colorado, the lanceleaf cottonwood should not be planted under power lines as it quickly grows to heights of up to 60 feet.
With its dense foliage, it is often planted as a windbreak. And, like all cottonwood trees, the leaves turn bright yellow in the fall.
The lanceleaf cottonwood is a relatively high-maintenance tree, so be prepared for pruning, cleaning up seeds, fruit, and broken limbs, and fighting off pests and diseases.
The lower branches can be pruned to allow pedestrians to pass beneath it. The best time to prune a lanceleaf cottonwood tree is in late winter after the threat of freeze has passed.
Note: Some cities/towns prohibit the planting of this tree because of its shallow roots and the many suckers that it produces.
Pest & Diseases to Watch For
Lanceleaf cottonwood can suffer from borers and canker disease.
It is also susceptible to aphids, scales, thrips, anthracnose, crown rot, mistletoe, and sooty mold.
However, cytospora canker is the biggest invasive threat to cottonwood trees, partially because the wood is already weaker than other types of trees.
Cytospora canker is a tree disease caused by several species of Valsa and Leucostoma fungi. The fungus attacks and kills the bark, causing dead or dying areas called cankers. In many cases, cankers can extend around an entire branch, cutting off water and nutrients to the rest of the branch and killing it. In severe cases, it can kill the whole tree.
Also called bacterial wetwood or bacterial slime, slime flux is exactly what it sounds like – a frothy slime that oozes out of trees, and then dries, leaving a white scum. The bacteria enters through cuts or wounds in the bark, such as from improper pruning cuts, lawnmower blad marks, or animal scrapings. One way to recognize slime flux is that it kills any grass it touches. Inside the tree, the bacteria eats and digests the wood, creating an internal pressure. This pressure is eventually relieved as the slime oozes through a crack in the tree’s bark.
We recommend spring or early fall planting to get your new trees off to a great start. You can always call us for advice on where to plant your new tree(s) and don’t forget that we offer professional tree planting services if you don’t want to do it yourself!
Recommended Trees & Shrubs
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Call us at 303-674-8733 or contact us online to get a free estimate for tree planting, general tree services or any aspect of our Plant Health Care program.