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Extension > Local Extension Offices > Stearns > County Horticulture Educator > Articles > Pruning Trees and Shrubs

Pruning Trees and Shrubs

University of Minnesota Extension, Stearns County News
January 25, 2017        
           
Source:  Beth Berlin, Extension Educator-Horticulture
University of Minnesota Extension
Stearns, Benton, & Morrison Counties


Pruning Trees and Shrubs
By Beth Berlin, University of Minnesota Extension

ST. CLOUD, Minn. (1/25/17) — This winter has been a swing of temperatures and everything from well below 0°F to unseasonably warm weather. Now that February is in sight it is time to consider pruning your trees and shrubs. An old rule of thumb was to prune in winter while the plant was dormant; well for best results we need to be a bit more specific than that. When to prune depends on the species, but for most, late winter into early spring is the best time to prune.

Pruning near the end of the dormant season has several advantages, including: 1) Limited time remaining before the tree or shrub will begin its spring growth and healing process 2) Avoid certain disease and pests 3) Provides easier sight and access without deciduous foliage.

Oak wilt can be a devastating disease and continues to spread throughout Minnesota and therefore oak trees should not be pruned during April, May, or June.  If an oak tree is damaged or wounded during this time period it is best to mask the cut with a wound dressing material to help minimize the attraction of pests that may spread the disease.

Fruit trees such as apples, crabapples, mountain ash, 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. 

Trees with sap will “bleed” during late winter or early spring pruning.  Although it may look alarming this does not cause harm to the tree.  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 one-quarter of the live foliage.

Early spring blooming trees and shrubs such as forsythia, flowering plum, lilac, azalea, chokeberry, chokecherry, and flowering crab should not be pruned in the late winter or early spring. Instead these early bloomers should be pruned after they have finished blooming.  If they are pruned at any other time, once the flower buds are set, you will be pruning off next spring’s flowers.

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.

Second, determine what branches should be pruned. Consider 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: 1) Crown thinning, selectively removing branches, specifically the weak, in the crown to promote air movement 2) Crown raising, removing the lower branches to provide more clearance for mowing, sidewalks, streets, etc. and 3) Crown reduction, 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 slightly above 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 size, prune back the six to eight inches of new growth. This form of pruning should be done in spring and again in mid-summer to give the hedge a dense and attractive appearance.

Remember that late winter and early spring is the best time to prune many of your trees and shrubs. Do your research, have the proper tools, and be careful.  For more information on pruning visit http://www.extension.umn.edu/garden/ and search for “pruning”.

Contacts

Beth Berlin
Extension Educator, Horticulture
(320) 255-6169
adam0062@umn.edu
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