Pruning at the proper time can help avoid certain diseases and physiological problems. Oak wilt can be a devastating disease and therefore oak trees should not be pruned during April, May, or June. The only time oaks should be pruned during these months is if the tree has sustained damage or is wounded, if this occurs it is best to apply a wound dressing to mask the fresh cut wood odor and not attract the beetles that spread the disease.
Fruit trees such as apples, crabapples, moutainash, hawthorns, and cotoneaster shrubs should be pruned in February through early April. This reduces the chance of the bacterial disease fireblight and infection from occurring. Pruning in fall or early winter may cause drying out and die-back at the pruning sites.
Shrubs grown for their foliage rather than flowers should be pruned in spring before their growth begins. Examples of foliage shrubs are barberry, burning bush (Euonymus), dogwood, honeysuckle, ninebark, and purple leaf sand cherry.
Early spring blooming trees and shrubs such as forsythia, flowering plum, lilac, azalea
chokeberry, chokecherry, and cherry should not be pruned in the late winter or early spring. Instead these early bloomers should be pruned after they have finished blooming in late spring. If they are pruned at any other time, simply you will be pruning off next spring’s flowers.
Some trees and shrubs will “bleed” during late winter or early spring pruning. Although it may cause alarm to the individual pruning, it will cause little harm to the plant. One option with these types of trees or shrubs such as maples, boxelders, birch, and walnut or butternut, is to prune them after their leaves are fully developed in late spring or early summer. However never remove more than ¼ the live foliage.
Pruning in late winter, just before spring growth, allows many trees and shrubs to only be exposed for a short period of time before new growth begins to seal over the wound. Another advantage of pruning at this time is that the branches are clearly visible without leaves obstructing the view.
Once you’ve determined the best timing to prune your trees or shrubs, it is important to know how to properly prune. First, it is critical to have the proper tool for the job, and ensure the pruner, lopper, or saw is sharp. Know the limitation of the tool, and use the proper sized pruner, or lopper, or instead use a saw.
Finally, we come to the question of “what should I prune?” Pruning should be done on young trees to remove: branch stubs, rubbing branches, water sprouts, sucker growth, closely spaced, and weak or narrow crotched branches. On established trees, the three most common types of pruning are crown thinning, crown raising, and crown reduction. Crown thinning is selectively removing branches, specifically the weak, in the crown to promote air movement. Crown raising, is simply removing the lower branches to provide more clearance for mowing, sidewalks, streets, etc. Crown reduction is removing some of the large branches at the top of the tree to reduce its height. This is not topping the tree because the branch is removed directly above the lateral branches. This form of pruning should only be done when absolutely needed.
In regards to pruning shrubs, up to one-third of the oldest, damaged, thickest stems or trunks should be pruned right to the ground. This technique will revitalize the plant and encourage new growth from the roots. Hedge pruning needs to be done often. After the hedge has reached the desired prune back the six to eight inch new growth to within two inches of the last pruning. This form of pruning should be done in spring and again in mid-summer to give the hedge a dense and attractive appearance.
Although there can be so many questions surrounding the task of pruning, it shouldn’t be intimidating. Do your research, have the proper tools, and be careful. Get pruning! Late winter and early spring are a great time to prune many of your trees and shrubs. For more information on pruning visit http://www.extension.umn.edu/garden/