Editor’s note: This is the third of a three-part series on pruning trees and shrubs.

One of the most joyful sights each spring is the emergence of new growth on woody plants, whether trees, shrubs or vines. In the landscape setting, gardeners employ pruning to keep plants healthy and attractive. Two previous articles addressed the rationale for pruning and the proper tools for the job. Now you’re ready to properly prune your woody plants. This article will describe:

• The proper way to make a cut.

• Types of pruning cuts and their effects on plant growth.

• Seasonal guidelines for pruning woody plants.

• Resources for information on pruning specific plants.

Proper cut

The proper way to make a cut is illustrated in Figure 1. Cut ¼ inch above the bud at a 45-degree angle. Prune to an outward facing bud to encourage growth away from the center of the plant, resulting in a more graceful shape.

Pruning cuts

The primary types of cuts include:

• Heading (Figure 2) – selective pruning of a terminal shoot or branch back to a lateral bud. This type of cut stimulates growth at the tips of the branches. However, excessive tip growth shields the interior of the plant from light penetration and air movement. Over time, and with repeated heading back, the plant develops a “dead zone” of woody stems that don’t produce any new growth. This type of pruning results in high-maintenance plant care.

• Shearing – a type of heading cut, but without regard to where the cuts are made along the branch. Shearing is used to create topiaries and the geometric shapes often found in formal gardens.

• Thinning (Figure 3) – removing a branch or stem where it joins another branch. This technique allows light and air to penetrate throughout the plant. In addition, proper thining retains the plant’s natural growth habit. This type of pruning is suitable for virtually any woody plant.

• Renewal – removing a portion of the oldest stems at ground level. This opens the interior of the plant to light and air movement. Complete renewal pruning is a three-year process. One-third of the oldest stems are removed in late winter to early spring. The following year, another third of the oldest stems are removed at ground level. Year 3 concludes with the remaining third of the old stems being removed. Renewal pruning results in complete renovation of the plant. This technique can be used on many plants and is particularly valuable for controlling large, overgrown shrubs.

• Rejuvenation – removing all stems down to 4-12-inches above the ground. This technique results is a completely new plant for the growing season. Plants such as, red-twig dogwood, spirea, forsythia and butterfly-bush can withstand this drastic pruning.

Shrubs are the best candidates for DIY pruning because they are more forgiving of improper pruning. Shearing shrubs whose natural habit is sprawling or upright and multi-branched into tight specimens diminishes their natural beauty.

If pruning is required for a young or mature tree, consult an arborist, nursery personnel or an experienced gardener. Improper pruning can result in a permanently disfigured tree, leading to insect, disease and structural problems in the future. Do not attempt to shear or prune a tree whose mature size ranges in the 40-100 foot range into a specimen suitable for a small garden.

Seasonal guidelines

Some “rule-of-thumb” guidelines:

• Know the genus, species and cultivar of the plant you are pruning. Consult the plant tag or research its mature size. Know when it blooms as well as if it flowers on old or new growth.

• Dead and broken plant parts can be removed anytime of the year.

• Diseased plant parts should be removed as soon as possible. Disinfect pruners when working with diseased tissue.

• If a plant has crossing branches that rub against each other, remove one of the branches to prevent insect/disease entry points.

• If a plant blooms in spring (March through May), wait until after blooming is completed to prune. Examples include rhododendron, forsythia, lilac and mockorange.

• Plants that bloom in summer or fall are best pruned in March through early April. Examples include abelia, butterfly-bush, caryopteris and some spireas.

• Hydrangea, clematis and roses have varying pruning schedules beyond the scope of this article. Use the resources below to explore specific plants and their pruning needs.

Pruning resources

• Internet, garden nurseries, experienced gardeners.

• Any Penn State Extension Office – for Allegheny County, call 412-473-2600.

• Two excellent publications from Penn State Extension include: http://extension.psu.edu/publications/agrs-095 and http://extension.psu.edu/natural-resources/forests/urban-community/publications/pruning-landscape-trees

• A good reference book covering all aspects of pruning is “The Pruning Book” completely revised and updated by Lee Reich.

Steve Piskor is a Penn State Master Gardener and a PA Certified Horticulturist. Columns by master gardeners will sometimes appear in place of the Garden Q&A by Sandy Feather, a Penn State educator.

First Published: April 18, 2015, 3:19 p.m.