Aspens, with their slender trunks, graceful leaves and dainty size, are visually appealing to home gardeners. Despite their beauty, though, they are not hardy trees and can suffer from a number of problems, according to Robert Cox, a horticulturist with Colorado State University. For that reason, home gardeners who undertake to grow aspens should be thoughtful about the care and culture of these trees.
Aspens need exposure to at least six hours of sunlight a day, and preferably more. These trees thrive in full sun but their fragile leaves can be scorched by very hot afternoon sunlight, so it's best to plant them in a location where they will receive morning sun, but will be somewhat protected by dappled or filtered afternoon shade.
There are many species of aspens that can grow in a wide variety of climates, but they all typically thrive in temperate climates with cool summers and mild winters. Aspens grow best in United States Department of Agriculture hardiness zones 1 through 7 (see Resources).
Aspens require moist, well-draining and slightly acidic soil for growth. Clay and other heavy soils are not suitable. If you have heavy soil, amend it with peat moss and sand in as large an area as possible before planting the tree. Trees that are already established will benefit from an application of acidic mulch to a depth of at least 2 inches and out to the canopy line of the tree. Do not let the mulch touch the trunk of the tree, since it can lead to fungi development.
Aspens can get stressed (weakened) easily by hot and drying winds, so they should be grown in protected areas. Ideal locations are the east or north sides of a house, where exposure to the sun is limited during the hottest hours of the day and where the walls can shelter the tree from strong winds. Young saplings should be supported by a wooden stake.
Pests and Diseases
Insects are a major problem for aspens. Boring insects are common in the soft wood, and many of these insects carry fungal disease, which can enter the tree as the insects bore. The fungi can then infect the heart wood of the tree, causing cankers to form and girdle the tree, which can cut off the flow of nutrients to parts of the tree. Branches that develop cankers--dry, dark, cracked areas of dead wood--should be pruned to prevent the spread of disease. A systematic application of fungicide in the spring can help reduce the chance of the tree developing a fungal infection. Monitor aspen trees consistently for insects and treat them with a thorough application of insecticide if an infestation is present.