Quaking aspen (Populus tremuloides) are lovely in the wild, and enjoy the most extensive native range of any tree on the continent. Their leaves have flattened petioles, so they tremble in every light breeze. You may have admired aspens lighting up park slopes with brilliant yellow fall color. But be sure to read up on quaking aspen tree facts before you plant them in your backyard. Cultivated aspens can be a problem to a homeowner. Read on for information about the pros and cons of planting a quaking aspen tree, and how to grow quaking aspen trees.
I. Appearance and Characteristics
Populus tremuloides is a deciduous tree native to cooler areas of North America, one of several species referred to by the common name aspen. It is commonly called quaking aspen, trembling aspen, American aspen, mountain or golden aspen, trembling poplar, white poplar, and popple, as well as others.
The quaking aspen is a tall, fast-growing tree, usually 15–18 meters (50–60 ft) at maturity, with a trunk 25 centimeters (10 in) in diameter; records are 36.5 m (119 ft 9 in) in height and 1.37 m (4 ft 6 in) in diameter. The bark is relatively smooth, whitish (light green when young), and is marked by thick black horizontal scars and prominent black knots. Parallel vertical scars are tell-tale signs of elk, which strip off aspen bark with their front teeth.
The leaves on mature trees are nearly round, 4–6 cm (1+1⁄2–2+1⁄4 in) in diameter with small rounded teeth, and a 3–7 cm (1+1⁄4–2+3⁄4 in) long flattened petiole. The leaves are green above and gray below. Young trees and root sprouts have much larger (10–20 cm, 4–8 in long), nearly triangular leaves. (Some species of Populus have petioles flattened partially along their length, while the aspens and some other poplars have them flattened from side to side along the entire length of the petiole.)
Aspens are dioecious, with separate male and female clones. The flowers are catkins 4–6 cm (1+1⁄2–2+1⁄4 in) long, produced in early spring before the leaves. The fruit is a 10 cm-long (4 in) pendulous string of 6-millimeter (1⁄4 in) capsules, each capsule containing about ten minute seeds embedded in cottony fluff, which aids wind dispersal of the seeds when they mature in early summer. Trees as young as 2–3 years old may begin seed production, but significant output starts at 10 years of age. Best seed production is obtained between the ages of 50 and 70 years.
Quaking aspen grows more slowly in the dry conditions of western North America than it does in the more humid east and also lives longer—ages of 80–100 years are typical, with some individuals living 200 years; the root system can live much longer. In the east, stands decay faster, sometimes in 60 years or less depending on the region.
Populus tremuloides is the most widely distributed tree in North America, being found from Canada to central Mexico. It is the defining species of the aspen parkland biome in the Prairie Provinces of Canada and extreme northwest Minnesota.
It grows at high altitudes as far south as Guanajuato, Mexico. It grows in isolated areas in northeastern Mexico as well as Baja California, Jalisco, the State of Mexico, Michoacán, Sinaloa, Sonora, and Veracruz.
Quaking aspen grows in a wide variety of climatic conditions. January and July average temperatures range from −30 °C (−22 °F) and 16 °C (61 °F) in the Alaska Interior to −3 °C (27 °F) and 23 °C (73 °F) in Fort Wayne, Indiana. Average annual precipitation ranges from 1,020 mm (40 inches) in Gander, Newfoundland and Labrador to as little as 180 mm (7 inches) in the Alaska Interior. The southern limit of the species’ range roughly follows the 24 °C (75 °F) mean July isotherm.
In the sagebrush steppe, aspens occur with chokecherry, serviceberry, and hawthorn, forming a habitable haven for animal life. Shrub-like dwarf clones exist in marginal environments too cold and dry to be hospitable to full-size trees, for example at the species’ upper elevation limits in the White Mountains.
II. How to Grow and Care
Sunlight
Grow quaking aspen tree in full sun for best results, although it does tolerate some shade.
Temperature and Humidity
Quaking aspen is cold-hardy all the way to zone 1. The tree will not handle heat and humidity well. It is not suited to regions such as the American Southeast.
Watering
For best results, keep the soil evenly moist. A quaking aspen should get a deep watering every two to four weeks. During hot summers, it should have water at least every other week. In winter, the tree needs water at least once a month if snow isn’t already on the ground.
Soil
Provide quaking aspen with good drainage. An average garden loam is sufficient.
Fertilizing
Quaking aspen performs best in moderately rich soil. Fertilize it with a complete fertilizer in early spring for an extra boost. Follow the instructions on the fertilizer package precisely. The instructions will spell out how much fertilizer to use, which varies according to tree size. Over-fertilizing can burn your plant.
Pruning
The best time to prune quaking aspen is winter because this is when the tree is dormant, meaning the tree will tolerate cuts better. Quaking aspen must be pruned after heavy winter snowfalls have damaged limbs. The damaged limbs should be pruned back to the collar. Dead or diseased branches should be pruned off whenever you spot them.
The only need for discretionary pruning is generally when growing the tree in an area where you will be walking regularly. You may wish to remove low-lying limbs there (rather than having to duck under them when walking). Again, prune such branches back to the collar.
Propagation
Quaking aspen spreads naturally through its root system, developing into large stands over time. In such a stand, one tree is a clone of the next. The trees are also dioecious, with distinct male and female colonies. Because quaking aspen trees propagate readily through their root systems, you can take advantage of this fact to acquire new trees. This is by far the easiest way to propagate quaking aspen. Take these easy steps:
- Simply dig up offshoots from the original tree.
- Transplant them to a suitable location in your landscape.
- Water regularly until established.
How to Grow From Seed
You can also grow it from seed, but it’s more troublesome. If you go this route, at least simplify matters by buying the seed rather than trying to harvest it from the wild. The latter is difficult for beginners because the pollinating male plants don’t look much different from the seed-bearing female ones (both produce catkins).
Once your seeds arrive, take these steps:
- Fill a planting container with moistened seed-starting medium.
- Sow the seeds right on top of the seed-starting medium; don’t cover them with soil.
- Keep the medium moist; placing the container in a plastic bag will help trap moisture. Seeds will germinate in 24 hours.
- Place the container in a window for light.
- Plant outdoors after all danger of frost has passed.
Pests and Diseases
Common Pests & Plant Diseases
Quaking aspen is susceptible to infestations of poplar borers. The larvae do the boring, and their holes invite damaging fungi into the tree. But these beetles typically attack trees that are in poor health. Thus the best control measure is to keep your tree in good health by ensuring its light levels, irrigation, and drainage, are adequate.
Quaking aspen can be attacked by powdery mildew disease. Quaking aspen likes evenly moist soil, but you must strike the right balance between dry and soggy soil. Soggy soil invites fungal infections. Likewise, don’t get the leaves wet when watering. Water early in the day so that excess water evaporates before nightfall. Practicing good garden hygiene can also help prevent this fungal disease. Remove and dispose of any diseased leaves or branches.
Common Problems
Quaking aspen is a very high-maintenance tree. Stay aware of these signs that indicate the tree may be in trouble.
Browsing Animals
Quaking aspens are a favorite food source for deer and elk. The animals seriously damage aspen trees by eating the shoots of young suckering trees and they eat the bark. Deer and elk also rub their antlers against the bark causing deep gashes that can kill the tree. The most significant damage occurs during the mating season (September to November).
To reduce tree damage, use strong barrier fencing to keep animals out. You can also wrap bark in rigid plastic, reducing damage, although a large elk can still damage or destroy a wrapped tree. Remove all wraps in the spring.
Leaves a Mess
Quaking aspens are among the prettiest trees but are also messy in terms of their maintenance. You must continuously remove the suckers or new shoots from their spreading root system.
Bark Discolored or Falling Off
Sunscald can cause a quaking aspen’s bark to become discolored, crack, fall off, or sink into the trunk. This condition occurs during winters with freezing weather dotted with unseasonably warm days. The warmth might confuse the tree, thinking it should come out of dormancy and prepare for spring growth. However, when the cold returns in full force in a few days, the tree isn’t dormant and prepared to handle the cold properly.
If your area experiences winters with frequent unseasonable warm snaps, consider painting the trunk with white latex paint to deflect sun rays. Also, make sure your aspens are receiving ample water. Drought-stressed trees are more likely to suffer from sunscald. If your tree has already been damaged from sunscald, do not paint the damaged bark sections. Allow it to heal.
Browning of Leaves
Browning leaves can be a sign of aspen leaf scorch, caused by aspens not getting enough water during hot and dry periods. There’s no quick fix or cure. Maintaining a watering schedule is the best way to bring your tree back to health. During the growing season, these trees need infrequent but deep watering. In the winter, ensure these trees get a deep soaking at least once a month (if no snow is on the ground).
Pale Yellow or Light Green Leaves
Your soil might have an iron deficiency if green leaves start turning pale green or yellow unseasonably soon, like in the summer. This condition is called chlorosis. You might notice the yellowing beginning at the edge of the leaves and then moving to the center. The leaf edges may turn brown, start curling, or fall off. If it’s an iron deficiency, the tree could benefit from chelated iron deep root injections into the soil around the tree. In extreme cases, injections into the tree might be needed.
III. Uses and Benefits
Aspen bark contains a substance that was extracted by indigenous North Americans and European settlers of the western U.S. as a quinine substitute.
Like other poplars, aspens make poor fuel wood, as they dry slowly, rot quickly, and do not give off much heat. Yet they are still widely used in campgrounds because they are cheap and plentiful and not widely used in building lumber. Pioneers in the North American west used them to create log cabins and dugouts, though they were not the preferred species.
Aspen wood is used for pulp products (its main application in Canada) such as books, newsprint, and fine printing paper. It is especially good for panel products such as oriented strand board and waferboard. It is light in weight and is used for furniture, boxes and crates, core stock in plywood, and wall panels.
