Regional Gardening Reports :: National Gardening Association

In the Garden:
Western Mountains and High Plains
February, 2009
Regional Report

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Aspens begin to bud with the spring-like weather.

Are Aspen Trees in Your Future?

Aspen trees are a favorite 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 landscapes at lower elevations with drier conditions;heavy, clay soils; and water restrictions.

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, spider mites, and diseases.

In you decide to plant a grouping of aspen trees -- and who doesn't want to replicate a piece of the mountains in their backyard -- then I highly recommend that you plan on planting young trees in the spring. This is the best time to ensure strong and healthy root development.

It is very important to choose the right location for success with aspens. Site trees in full sun in 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 that you 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 it begins to runoff, then move the sprinkler to another location until you have completed soaking around the root zone. And don't forget about watering during the open, dry conditions of winter. In my area, temperatures have been in the mid-50s and low 60s for several weeks already, and it's not even close to spring. We sure need some moisture from Mother nature.

If you already have aspen trees in your yard it is not unusual at this time to see a variety of problems showing up. As the weather warms, you may notice signs of discoloration on the bark. As the days begin to get longer you may see an amber colored sap oozing from the branches and on the main trunk. These are often the symptoms of a disease known as cytospora canker.

The symptoms of cytospora 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 typical pinhead-sized black speckles or "pimples." In the spring, these pimples produce spores (the fruiting bodies) which ooze out as coiled, thread-like, orange tendrils. This allows the disease to spread to open wounds and continue the disease cycle.

Once infection occurs, the most reliable treatment is to increase tree vigor and practice good sanitation procedures. Prune or remove infected branches, stems, and other areas. Make smooth, clean cuts at the base of diseased branches, as near the trunk as possible, but without damaging the branch collar (swollen region at the base of the branch). It may be necessary to remove an entire tree if it is severely infected. Prune when the weather conditions are dry. Clean pruning wounds to prevent further spread of the disease. Use rubbing alcohol, ethyl alcohol, or a spray disinfectant.

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