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Ag Matters column: Solving the evergreen pruning puzzle

Homeowners are often concerned about the proper timing and pruning technique for the evergreen trees and shrubs on their property. Most evergreens cannot replace lost growth common with deciduous plants. Other landscape plants may be able to outgrow a bad pruning job but evergreens can suffer permanent disfigurement.

With the exception of those that have been pruned into formal or artificial shapes, evergreens require little pruning. It is important to note that the different species of evergreens should be pruned according to their varied growth habits.

The pruning puzzle arises from the fact that there are few pruning recommendations that fit all evergreens as a group.

A major concern is the proper pruning time for foundation evergreens shrubs. Arborvitae, junipers, yews and hemlocks grow continuously throughout the growing season and can be pruned anytime from the time they begin to put out new growth in the spring until early August. Avoid pruning evergreens in the fall as pruning will encourage new growth that will not harden off properly leading to winter injury.

A common question is in regard to the possibility of cutting off pyramidal arborvitae or junipers that have become overgrown. These shrubs will survive, but they will never regain their pyramidal form. They will be flat-topped and quite unattractive. In these cases, it is best to remove and replace them. These plants will tolerate heavy shearing, but they should be pruned only to control size or correct growth defects. Periodic shearing of these shrubs throughout the growing season is the best way to control size while maintaining a neat appearance.

Spruces, firs and Douglas firs do not grow continuously but can be pruned at anytime because their lateral buds will sprout if the terminal buds are removed. The pruning cuts should be made just above a side bud or branch to avoid stubs. Do not prune the branches back to bare wood because there are no buds to produce new growth and the branch will die. It is recommended that they be pruned in late winter, but they will tolerate some spring pruning.

Pines put out a single flush of tip growth each spring and then stop growing. Pines seldom need pruning except to encourage dense growth. Any pruning that is done must occur when the new growth is in the "candle" stage.

Mugho pine used as foundation plantings, for example, can become overgrown and gangly looking if not pruned to control their size and make them appear to have greater density. Pines do not have lateral buds, so removing the terminal buds will not produce new growth and will eventually result in dead stubs.

Pruning must consist of removing up to two-thirds of the candle, which will reduce the growth of the branch and encourage buds at the base of the candle to put forth new growth.

The lower branches of spruce, especially Colorado spruce, often become diseased and are often removed to prevent further spread of the needle diseases. These branches can be removed from pine or spruce trees any time of the year, although it produces some stress on the tree when they are removed while the tree is candling. Remember, these branches will never grow back.

For more information, contact me at the Polk County office in McIntosh or at the Clearwater County office on Wednesdays. Our toll free number is 800-450-2465. If e-mail is your thing, contact me at

Source: Carl Hoffman, Stearns County Extension Service.