Aspen trees are an alpine tree that grow in the Rocky Mountains, among other places. In some cases, nurseries will dig trees and bring them down to lower elevations for ornamental growth. In their natural environment, aspens are easy to care for. However, when brought down to lower elevations, they need a little more care than other trees.
Aspen trees prefer light, acidic soil that drains well. If you are planning on planting aspen in a heavy clay soil, build a berm of sandy loam 18 to 24 inches high and plant your trees in that berm. If planting aspen in an urban area, be aware that most aspen are dug from mountainous areas, leaving them with reduced root balls that might have trouble with compacted urban soils.
Aspen trees are often the tallest tree in their natural mountain environment. Aspens need full sun to thrive. Aspens reproduce via clonal roots, meaning new trees sprout from the root of an existing tree. As aspen groves grow in, the number of aspen sprouting below the canopy drops dramatically.
Aspen do best in cool, dry summers in areas that get abundant winter precipitation in the form of snow. When growing aspen in urban or cultivated landscapes, follow a watering schedule of 2 to 3 inches of water per week. However, if you start to have problems, consult a county agricultural extension to re-define the schedule for your local microclimate. Aspen can have trouble with too much water or too little water.
Problems such as leaf spot can sometimes be reduced by fertilizing an aspen with a balanced fertilizer. When selecting a fertilizer, follow the instructions on the package to prevent over-fertilization. Do not fertilize in the fall, as this could trigger new growth that will not allow the tree to harden off properly for winter.
Aspen is susceptible to a number of diseases. Some of the diseases have no known controls or treatments. Blackened leaves at the end of summer or fall are caused by aphid secretions. This disease is called aspen leaf spot disease or Marsonnina leaf spot disease. The best control is to remove the affected leaves or branches in the fall and to remove branches to increase air circulation through the tree. Orange pimples on the branches indicate cytospora canker. The only treatment for cytospora canker is to remove the branch.