Pruning Basics

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Structure. The visual backbone to every landscape. Trees and shrubs are perfect for aesthetic value and structural interest. Each specimen brings its own beauty, interest and character to its surroundings. Branching habits and natural forms make any homeowner want the perfect fit for their landscape. But what does that mean as a reality in terms of maintenance? Just because a plant is a great fit, it requires upkeep to stay that way.

Pruning is the selective removal of plant parts (branches, buds, roots). When evaluating what to prune, we first recommend establishing a pruning objective so the process remains clear when removing plant material. Here are a few examples of pruning objectives: reduce risk of failure, provide clearance, reduce shape and wind resistance, maintain or improve health, influence flower and fruit production, improve view, improve aesthetics, increase life span, and repair or correct damage.

One of the most important objectives is reducing risk of failure by creating, maintaining, and developing strong structure. Look out for the three D’s: dead, diseased, and damaged. These are important because prompt action aids in plant health. Appropriate pruning cuts improve chances of recovery and give way to safe, structurally sound specimens. Pruning should be performed at regular intervals, starting when a tree or shrub is young and continuing into maturity. Removing undesirable plant growth on a regular basis will prevent the need for extensive pruning on an irregular basis. 

When to Prune 

Determining when to prune is important and varies depending on the plant. Removing diseased, injured, or dead wood from any tree or shrub can be done year around. Lightpruning can be performed on small-diameter branches following a flush of growth after leaves harden and turn dark green, usually in late spring or summer. Pruning any heavier than that in the summer can wound the plant as open cuts are prone to pests and diseases. Late-summer or early-fall pruning may stimulate new growth. If the growth does not harden off before a heavy frost, new stems or branches will still be tender and may be killed. Generally, heavy pruning or large cuts should wait until deciduous plants are dormant in late fall to early spring.

The majority of flowering trees and shrubs bloom on old wood. They should be pruned after flowers start to fade in late summer. Branches will have a chance to produce new growth where next year’s flower buds will form. Keep in mind that pruning immediately after flowering removes fruits for summer and fall. Some flowering trees and shrubs bloom on new wood and should be pruned in late winter when they go dormant before new growth develops. Flowers will emerge after new growth. Before you prune your flowering plant, it is important to know what kind of wood it blooms on to ensure it produces flowers.  

The garden center often gets questions about pruning hydrangeas. The most important factor with hydrangea pruning is knowing the species. Bigleaf hydrangeas (Hydrangea macrophyllaand H. serrata), and oakleaf hydrangeas (H. quercifolia) flower on old wood. Panicle hydrangeas (H. paniculata) and smooth hydrangeas (H. arborescens) flower on new wood.

Conifers usually require little pruning. Do not prune live branches in late spring through summer. This is the growing season and sap is flowing. Bark on conifers is easily damaged and there is a higher risk of fungal infection at this time. Late winter and early spring are ideal for evergreen pruning. Pines, however, are the exception. Pines have buds at the tips of their branches. If a branch tip is pruned off after a growth flush, then the terminal bud is removed and regrowth is impossible. Early summer is ideal for pines because when a new branch (candle) begins to elongate, it can be pinched. This pruning leads to dense and compact growth, but still allows buds to form for the following year. 

Junipersarborvitae, and similar species have dense growth characteristics. Because of this, a dead interior zone is common where twigs and buds are killed from lack of sunlight. The dead zone limits the extent of pruning because if it is exposed, new shoots will not develop and the result is a deformed plant with an unsightly brown spot. 

Two Basic Pruning Cuts

There are two basic types of pruning cuts: heading and thinning. These cuts cause plants to grow in different ways.

  1. Heading: Cutting a stem back to a bud, twig, or stub. A few potential problems may arise with heading cuts. A stub is often left and may become infested with insects or diseases. Heading stimulates vigorous, new growth and these shoots may be weakly attached, causing splitting or cracking when under pressure. Heading cuts also tend to destroy the natural shape of a plant.
  2. Thinning: The removal of a branch to its point of origin or point of attachment. This results in fewer branches growing near where the cut is made. The plant retains its natural form, light is more accessible to inner foliage, and vigorous shoot growth is not induced. Removing more than 30% of plant material with this pruning style can stimulate unwanted new growth. Thinning is the preferred method of pruning.  

Location of Pruning Cut

Determining the location of a pruning cut is very important. Plant health and strength are directly influenced by cut location. The size of a twig or limb dictates the placement of a pruning cut. If you are heading, cut twigs and small branches back to a bud directed away from the plant’s interior. Make the cut approximately one-quarter inch above the bud and slant the cut away from the bud. Cutting at an angle allows any water or moisture to run off the open cut rather than pool or sit. Sitting moisture on an exposed cut may cause or invite disease. If you are thinning, prune down to a lateral branch.

If you are cutting limbs on trees or mature, large shrubs avoid pruning too close to the trunk or leaving a stub. Before you cut, locate the branch bark ridge. This is the raised area of bark where the branch attaches to the main trunk. Then, note where the branch collar is located. This is the swollen region on the bottom side of the branch where it joins with the trunk. The bark ridge and branch collar prevent diseases from entering and spreading throughout the tree. It is important to not damage this area. Support the branch as you cut to prevent the bark from tearing or peeling.

Limbs too heavy to support by hand should be removed with the three cut method. This method is used to avoid splitting the branch or tearing into the bark. The first cut is made on the underside of the limb–approximately 12 inches out from the branch collar. Cut at least one-quarter of the way through the branch. The second cut is made on the top branch about one inch farther out from the undercut. Cut all the way through. The third and last cut is made on the top side, just outside of the branch bark ridge to remove the remaining stub.

Evaluate 

When you begin pruning it is important to evaluate as you go. Here are a few tips to keep in mind throughout the pruning process. Evaluate what needs to be removed and why. Every cut should be justified.

  1. Determine why the tree or shrub needs pruning — what are your pruning objectives?
  2. Step back from the specimen and look at it as a whole
  3. Visualize the plant five years, ten years, and thirty years from now
  4. Remember the 3 D’s (dead, diseased, damaged)
  5. Select the branches and stems to be removed or shortened
  6. Cut with proper pruning methods and tools*

*Tools should always be sharp and clean when pruning

Pruning dosage, or the severity of how much foliage is removed, is also important when evaluating a plant. Dosage is directly correlated to plant age. Removing any more than the recommended pruning dose percentage could injure your plant.

Pruning gives way to safe, structurally sound specimens, increases ornamental value and quality, stimulates growth and encourages desirable habits, and induces flowering and fruiting. Regular tree and shrub maintenance enhances the natural forms each specimen has to offer. Many woody plant species are suitable for Idaho and the Treasure Valley. Franz Witte is passionate about finding the perfect fit for your landscape. Stop into the garden center and shop our selection of plants, each with its own unique habit, form, and character.

By Riley Rehberg

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