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, this duet of colors may be reversed. Either way, when you are in that part of the country, these natural wonders are your frequent companions. But it may be best to admire their beauty in nature rather than trying to grow them in your landscaping.
Botanical Facts, Fall Foliage of Quaking Aspen Trees
Quaking aspen trees (botanical name Populus tremuloides, and also commonly called "trembling aspens") have a golden-yellow fall foliage color, after bearing deep-green leaves all summer. 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 these deciduous trees provide.
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 to 50 feet at maturity, with a spread of 10 to 30 feet in the canopy.
These autumn specimen plants are members of the willow family. They are closely related to poplar trees, such as Lombardy poplar trees (Populus nigra). Like their willow-family relative, the pussy willow (Salix discolor), quaking aspen trees bear catkins in the spring (these serve as their flowers) and are dioecious.
Another relative is the eastern cottonwood (Populus deltoides), which gets its common name from the fuzzy hairs attached to its seeds. This "cotton," which blows in the wind, is a mechanism used by the plant to disperse its seed, a mechanism also used by dandelions (Taraxacum officinale), for example. But eastern cottonwood is a much taller tree than quaking aspen, often reaching heights of 80 feet or more.
The bigtooth aspen (Populus grandidentata) is so called because the ridges (or "teeth") that run along its leaf margins are much bigger than those on quaking aspens. This is another relative that grows taller than quaking aspen: 50 to 80 feet.
Silver-leafed popular (Populus alba) has a different angle. Instead of offering autumn gold, it features silvery leaves during the summer.
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 soil amendments.
If you live in areas where beavers reside, you will have to protect your quaking aspen trees by wrapping the trunks in fencing. 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:
Interesting Facts About Quaking Aspen Trees
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. What you are hearing is the beating of leaves, as they shake and slap against each other.
The influence of quaking aspen trees in the American West 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 became the state tree of Utah in 2014. The state library's site 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."
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.
Where They Grow, How They Grow, and a Warning
This lover of the cold weather does best in USDA plant hardiness zones 1 to 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 could be a good choice when you need a fast-growing tree (and a lot of space to fill), something that will put on height quickly and spread. But it is not a good choice for small yards, where well- behaved plants work better.
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.
For the same reason, avoid growing quaking aspen trees around hardscape structures. For example, their root systems can damage public sidewalks and private walkways, alike. If you value their autumn color, there are many trees with great fall color that are better choices for your yard than quaking aspen. Types with golden leaves include: