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Extension > Garden > Yard and Garden > Pruning trees and shrubs

Pruning trees and shrubs

Mike Zins and Deborah Brown, former Extension Horticulturists

Revised 2014 by Gary Johnson and Gary Wyatt

Pruning is a horticultural practice that alters the form and growth of a plant. Based on aesthetics and science, pruning can also be considered preventive maintenance. Many problems may be prevented by pruning correctly during formative years for a tree or shrub.

Reasons for pruning

Prune to promote plant health

Avoid topping trees. Removing large branches leaves stubs that can cause several health problems. It also destroys the plant's natural shape and promotes suckering and development of weak branch structures.

Prune to maintain plants; intended purposes in a landscape, such as:

Prune to improve plant appearance

Appearance in the landscape is essential to a plant's usefulness. For most landscapes, a plant's natural form is best. Avoid shearing shrubs into tight geometrical forms that can adversely affect flowering unless it needs to be confined or trained for a specific purpose. When plants are properly pruned, it is difficult to see that they have been pruned! Prune to:

Prune to protect people and property

Pruning begins at planting time

Pruning is really the best preventive maintenance a young plant can receive. It is critical for young trees to be trained to encourage them to develop a strong structure. (See Figure 1)

Young trees pruned improperly or not pruned at all for several years may require heavy may require heavy pruning to remove bigger branches to prevent trees from becoming deformed.

At planting, remove only diseased, dead, or broken branches. Begin training a plant during the dormant season following planting.

Pruning young shrubs is not as critical as pruning young trees, but take care to use the same principles to encourage good branch structure. Container grown shrubs require little pruning.

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Figure 1. Issues to watch for when pruning trees

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Figure 2. How to cut when pruning a small branch or twig

Pruning large established trees

Leave the pruning of large trees to qualified tree care professionals who have the proper equipment. Consider the natural form of large trees whenever possible. Most hardwood trees have rounded crowns that lack a strong leader, and such trees may have many lateral branches.

The most common types of tree pruning are:

Proper branch pruning

Pruning large branches

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Figure 3. How to remove large branches using multiple cuts

Timing

The late dormant season is best for most pruning. Pruning in late winter, just before spring growth starts, leaves fresh wounds exposed for only a short length of time before new growth begins the wound sealing process. Another advantage of dormant pruning is that it's easier to make pruning decisions without leaves obscuring plant branch structure. Pruning at the proper time can avoid certain disease and physiological problems:

Pruning at the proper time can avoid certain disease and physiological problems:

Trees and shrubs that bloom early in the growing season on last year's growth should be pruned immediately after they finish blooming:

apricot
azalea
chokeberry
chokecherry
clove currant
flowering plum
or cherry
forsythia
Juneberry
lilac
magnolia
early blooming spirea

Shrubs grown primarily for their foliage rather than showy flowers should be pruned in spring, before growth begins:

alpine currant
barberry
buffaloberry
burning bush
dogwood
honeysuckle
ninebark
peashrub
purpleleaf sandcherry
smokebush
sumac

Shrubs that bloom on new growth may be pruned in spring before growth begins. Plants with marginally hardy stems such as clematis and shrub roses should be pruned back to live wood. Hardier shrubs such as late blooming spireas and smooth (snowball) hydrangeas should be pruned to the first pair of buds above the ground.

Pruning hedges

After the initial pruning at planting, hedges need to be pruned often. Once the hedge reaches the desired height, prune new growth back whenever it grows another 6 to 8 inches. Prune to within 2 inches of the last pruning. Hedges may be pruned twice a year, in spring and again in mid-summer, to keep them dense and attractive. Prune hedges so they're wider at the base than at the top, to allow all parts to receive sunlight and prevent legginess.

Renewal pruning for older or overgrown shrubs

Every year remove up to one-third of the oldest, thickest stems or trunks, taking them right down to the ground. This will encourage the growth of new stems from the roots. Once there are no longer any thick, overgrown trunks left, switch to standard pruning as needed.

Rejuvenation pruning for older or overgrown shrubs

Deciduous shrubs that have multiple stems (aka, cane-growth habit), and that have become very overgrown or neglected can be rejuvenated by cutting all canes back as close to the ground as possible in early spring. That season's flowers may be sacrificed but the benefits from bringing the plants back to their normal size and shape outweigh this temporary "collateral damage." This pruning technique works best for shrubs such as overgrown spirea, forsythia, cane-growth viburnums, honeysuckle and any other multiple stemmed shrubs that are otherwise healthy. Within one growing season, these shrubs will look like new plantings, full and natural shaped.

Pruning evergreens

With few exceptions, evergreens (conifers) require little pruning. Different types of evergreens should be pruned according to their varied growth habits.

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Figure 4. Pruning shears

Use the right tools for pruning

The right tools make pruning easier and help you do a good job. Keeping tools well-maintained and sharp will improve their performance. There are many tools for pruning, but the following will probably suffice for most applications:

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Figure 5. Lopping shears

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Figure 6. Hedge shears

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Figure 7. Hand saws



This publication is based on an earlier version written by Mervin Eisel, former Extension Horticulturist.

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