In the Garden:
Western Mountains and High Plains
August, 2005
Regional Report

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Aspens are beautiful and fast-growing trees, best planted in the proper location, such as this one, to prevent a cornucopia of problems. (Photo courtesy of David Sphan, The Tree Farm)

Selecting Aspen Trees for the Landscape

Aspens are one of the favorite, fast-growing trees in our region, with their smooth white bark, leaves that quake in the wind, and relatively fast growth rate. But wait; there are some limitations for their use in home landscapes. We might not always be able to create the proper conditions for this higher elevation species. It pays to know the needs of a tree before planting.

Ideal Conditions for Aspens
Aspen trees do best at elevations of 7,000 feet and above. When planted in lower elevations and in poorly drained clay soils, they are vulnerable to a wide range of problems, including insect pests and diseases.

If you decide to plant a grouping of aspen trees, I recommend you do so in the spring to allow time for them to establish good root systems over the summer. Site them in full sun in a well-drained soil that has been amended with compost, sphagnum peat moss, or a combination of the two amendments. The location should have very 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 aspen are shallow-rooted trees, I recommend watering 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 a plethora of diseases. One of the most fatal to the trees are canker diseases. The symptoms of Cytospora canker show up as reddish orange to blackened areas on the bark of the trunk and on branches. It is very common to see oozing sap in spring and fall. Advanced stages of the disease include sunken dead spots in the bark with the typical pinhead-sized black speckles or "pimples." In spring, these "pimples" produce spores (fruiting bodies) that ooze out as coiled, thread-like, orange tendrils. These spores spread the disease to open wounds and continue the disease cycle.

Treating Disease Problems
Once infection occurs, the most reliable treatment is to improve the vigor of the tree and practice good sanitation. Prune or remove infected branches, stems, and other areas. Make smooth, clean cuts at the base of diseased branches, as near to the trunk as possible but without damaging the branch collar (swollen region at the base of the branch).

Prune when the weather conditions are dry. Clean pruning wounds to prevent further spread of the disease, using rubbing alcohol, ethyl alcohol, or a spray disinfectant. It may be necessary to remove an entire tree if it is severely infected.

If you pick your trees wisely and choose the right tree for the right place, you'll be less likely to have serious problems with them. Trees are an investment in the future, so select ones that will last for many years to come.


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