In the Garden:
Western Mountains and High Plains
May, 2007
Regional Report

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Quaking aspens in the right location provide accents in the landscape.

The Allure of Quaking Aspen

It happens every spring around this time: questions abound about growing a regional favorite -- the quaking aspen. It is a very alluring tree, with its shimmering, heart-shaped leaves that tremble or quake in the lightest breeze. Quaking aspens are widely used in the home landscape, and they grow quickly, maybe too rapidly for some. But who can resist the bright yellow leaves in the autumn, so handsome against the white bark.

Aspens are closely related to poplar trees, such as Lombardy and Silver poplar trees, thus their rapid growth rate, extensive root exploration, and high water demand. Quaking aspen trees bear catkins in the spring. The female trees produces the fine cotton that's dispersed by the wind. In nature, quaking aspens are quick to spread into areas that were destroyed by fire. "Quick" is the enticement that makes landscapers choose this species when the homeowner needs a tree for height, and needs it fast! However, be forewarned: aspen trees can become invasive, with their powerful root systems sending out suckers everywhere in the landscape.

Keeping Trees Healthy
If you decide to plant a grouping of aspen trees, spring is one of the best times to plant. Select a site in full sun with well-drained soil. If your soil is clay, amend it with compost, sphagnum peat moss, or a combination of both these organic amendments. The planting site should have good air circulation to reduce the incidence of leaf diseases.

To keep aspen trees growing healthy and vigorously, don't let them become stressed. Provide weekly watering throughout the growing season, particularly during prolonged, hot, dry spells. Since aspens are shallow-rooted trees, water them with a frog-eye sprinkler placed at the dripline (the area where the outermost branches extend). Run the sprinkler for 15 to 20 minutes or until water begins to run off, then move the sprinkler to another location until you have completely soaked the root zone.

Aspen trees that have become stressed from drought, insect invasion, sunscald, herbicide injury, weed trimmer damage, defoliation by fungi, hail damage, or overwatering, are more susceptible to various diseases. One of the most fatal to the trees is canker. The symptoms of Cytospora canker show up as reddish orange to blackened areas on the bark of the trunk and on branches. It's very common to see oozing sap in spring. Advanced stages of the disease include sunken dead spots in the bark with typical pinhead-sized black speckles or "pimples." In the spring these pimples produce spores (the fruiting bodies) that ooze out as coiled, thread-like, orange tendrils. This allows the disease to spread to open wounds and continue the disease cycle.

It may be necessary to remove an entire tree if it is severely infected. Prune when the weather conditions are dry, and keep your pruning tools clean by disinfecting with 90 percent rubbing alcohol or a spray disinfectant.

Growing trees is not an exact science, but it does require an understanding of their specific growth habits and requirements. Just reviewing that information will help you select types that will meet your specific needs. Just remember, pick the right tree for the right place and you will be rewarded with beauty and shade for many years to come.


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