The Fall Foliage of Quaking Aspen Trees

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 About 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. 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.

Quaking aspens have a wider range than any other tree of North America, although they aren't found in the U.S, southeast region. 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. They are perhaps the dominant fall foliage tree of western North America, but New Englanders are also familiar with the autumn color that these deciduous trees provide.

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.

Relatives of Quaking Aspen

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, which 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, akin to 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 named for the ridges (or "teeth") that run along its leaf margins that are much bigger than those on quaking aspens. This is another relative that grows taller—50 to 80 feet—than quaking aspen.

Silver-leafed poplar (Populus alba) has a different angle. Instead of offering autumn gold, it features silvery leaves during the summer.

Potential Problems With Growing 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.

Unfortunately, numerous diseases and pests plague quaking aspens, including:

• Borers
• Cankers
• Leaf spot
• Powdery mildew
• Rusts
• Scale

Where and How They Grow

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. They are good landscaping choices when you need a fast-growing tree and a lot of space to fill since they will put on height quickly and spread. But it is not a good choice for small yards, where well-behaved plants work better.

If you value their autumn color, there are many trees with great fall colors that are better choices for your yard than quaking aspen. Types with golden leaves include:

• Sunburst honey locust (Gleditsia triacanthos var. inermis Suncole)
• Birch (Betula spp.)
• Shagbark hickory nut trees (Carya ovata)
• American beech (Fagus grandifolia)