Time to Prune Trees and Shrubs

Robert J. Souvestre  |  1/6/2012 7:22:12 PM

Pruning is one gardening job that is often neglected because gardeners are not exactly sure what to do. There is a great deal of confusion about how to prune, when to do it and even why pruning is done. As a result, pruning is often delayed until radical and extensive pruning is required. Now is an excellent time to evaluate your landscape for pruning that needs to be done, since many plants can be pruned now through February.

Hand pruners are your best tool. The bypass cut or scissor type pruners are the most useful. Anvil-type, hard pruners aren't as good as they tend to crush rather than cut limbs. Use lopping shears to prune small trees or shrubs with diameters up to 1 inch. For plants with branches more than 1-inch thick, use a pruning saw. Wound sealants or pruning paints are not recommended.

A wide variety of plants may be pruned during the winter and early spring, including most woody plants such as trees and shrubs, hedges, screens and foundation plantings that are not grown for their flowers. Both evergreen and deciduous plants may be pruned.

For trees and shrubs that are grown for their flowers, you must consider when they bloom before you decide to prune them at this time.

You should avoid extensive pruning of spring-flowering trees and shrubs (those that bloom from January through April), such as Japanese magnolia, star magnolia, silver bell, parsley hawthorn, Taiwan flowering cherry, quince, azalea, Indian hawthorn, deutzia, mock orange, spirea, banana shrub, wisteria and camellia. These plants have already set their flower buds for spring bloom, and any pruning done before they bloom will reduce the floral display these plants will produce.

On the other hand, summer-flowering trees and shrubs, such as crape myrtle, vitex, althea, oleander and abelia, do not have flower buds set on them now. These plants set their flower buds and will bloom on the new growth they produce in spring and early summer. As a result, they may be pruned during winter and early spring.

A few shrubs, including gardenia, hydrangea, some old garden roses and climbing roses, are in a category of their own. They bloom in early summer, but they have already produced their flower buds or flowering shoots for next year. Extensive pruning from now until they bloom will greatly reduce or eliminate flowering. Prune these plants in midsummer soon after they have finished blooming.

Once you have decided to prune, the real dilemma is how exactly to do it. Most gardeners feel they don’t know what they’re doing and they’re afraid of damaging or killing the plants they prune.

There is no simple answer. A book cannot tell you exactly how you should prune a particular plant in your landscape. Each plant is different, the desires and needs of each gardener are different, and each situation is unique. Advice such as “try to maintain the natural shape of the plant” is good, but not very helpful. You can, however, at least make sure you prune at the proper time. You can also become familiar with the basic pruning techniques we use to shape and control plants. Heading back involves shortening shoots or branches and stimulates growth and branching.

Heading back is often used to control the size of plants, encourage fullness, rejuvenate older plants and maintain specific shapes as in topiary and espalier. Often overdone by some gardeners, careless heading back can destroy the natural form of a plant in situations where the natural shape is desirable. Shearing is a specialized type of pruning that is done with a pruning tool called shears, which look like large scissors. A variation on heading back, this technique is used to create geometric shapes common in more formal landscape designs.

Shearing should not be used for general pruning purposes such as controlling size. The result will be clipped, formal shapes that require a lot of work to maintain.

Thinning out removes shoots or branches at their point of origin, either back to a branch fork or back to the main trunk. Thinning cuts can control the size and shape of a plant while doing a better job of maintaining the plant’s natural shape. Thinning cuts do not stimulate growth and often work more with the plant’s natural growth patterns to correct problems.

The only way to gain confidence in pruning is to do it. Practice makes perfect, as that saying goes. The first step to gaining confidence is to ask, and fully answer, two questions before pruning begins. First, why, specifically, do you feel this plant needs to be pruned? Or, what specific goal do you want to accomplish? What problem do you need to correct? If you can’t come up with a good reason to prune a plant, leave it alone. Second, how do you need to prune the plant to accomplish the goal? Study the plant carefully and decide what specifically needs to be done before you begin.
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