On an October day in the Rocky Mountains, you will sometimes find stands of quaking aspen trees that stretch for miles, their autumn gold perhaps punctuated here and there by the green of a conifer or two, as if for contrast. Elsewhere in the Rockies, this duet of colors may be reversed, as in the picture.
But the fact is, when you are in that part of the country, these natural wonders are your frequent companions. Their influence is everywhere. It is from the name of this fall foliage standout that the ski resort of Aspen, Colorado derives its name. Originally called Ute City, according to the city's website, it received its current name in 1880.
The quaking aspen (botanical name Populus tremuloides, and also commonly called the trembling aspen) became the state tree of Utah in 2014. The Utah State Library website states that it "replaced the Colorado blue spruce, which had held the honor of state tree since 1933," adding that it "makes up about 10% of the forest cover in the State of Utah and can be found in all of Utah's 29 counties."
Fall Foliage of Quaking Aspen Trees, Some Relatives, and Why They "Quake"
Quaking aspen trees have a golden-yellow fall foliage color. They are perhaps the dominant fall foliage tree of western North America, but folks in places such as New England, too are very familiar with the autumn color that they provide.
These autumn specimen plants are members of the willow family. They are closely related to poplar trees, such as Lombardy poplar trees. Like their willow-family relative, the pussy willow, quaking aspen trees bear catkins in the spring (these serve as their flowers) and are dioecious.
The origin of the name, "quaking" lies in the fact that the foliage of aspens shimmers or "quakes" when there is a breeze. This quality is due to the trees' flattened petioles, or leaf stalks. It is a poetic picture to imagine: a crisp blue sky, a grove of golden aspens and an autumn breeze, all working in concert to mimic a blazing sun shimmering across a deep blue sea. But instead of the rippling of waves, what one hears in this case is the beating of leaves, as they shake and slap against each other.
As if their fall foliage were not enough of a contribution, quaking aspens also have a lovely, whitish-colored bark that is quite smooth when they are young. Aspens usually reach a height of 20-50 feet at maturity, with a spread of 10-30 feet in the canopy.
Problems, Care of Quaking Aspen Trees
Grow quaking aspens in full sun and in consistently-moist but well-drained soil. Enrich the soil (and improve its drainage at the same time) by mixing in humus.
If you live in areas where beavers reside, you will have to protect your quaking aspen trees. Beavers will go to work on them before any other tree. The trade-off, in terms of wildlife, is that ruffed grouse and other birds prize the aspen's buds in winter as a food source.
Unhappily, numerous diseases and pests plague quaking aspens, including:
Where They Grow, How They Grow, and a Warning
Quaking aspens have a wider range than any other tree of North America. They are absent from the Southeast in the U.S., but they are found from Newfoundland and Alaska in the North as far south as central Mexico. But their greatest concentration is in Canada and the northern U.S. Indeed, this lover of the cold weather does best in USDA plant hardiness zones 1-6; it is not a good selection for areas with hot climates.
Quaking aspens spread through cloning to form a monoculture; this ability helps them naturalize readily. They are quick to spread into disturbed areas, such as areas devastated by fire, and quick to put on some height. "Quick" is the key term here for the landscaper, since these plants are a good choice when you need a fast-growing tree, something that will put on height quickly and spread.
However, the reason aspens take over a disturbed area so quickly is that their root systems are vigorous and aggressive. These powerful root systems will push up suckers everywhere. So be forewarned: You would not want to plant this tree around pipes, for instance, nor is it one of the good plants for septic tank drain fields.
Looking for more choices for fall color? See Fall Foliage Trees.