Pruning Hedges


“How low can I trim my hedges….if it depends on what kind they are can you point me to a good website. We didn’t trim last year….and you can bearly see the siding on my house, the plants are that high. They are a mix of evergreens and deciduous.  Thanks”

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Before you start to prune, have your endpoint in mind.  Pruning is one of the essentials in maintaining a landscape, but is one of the least understood of the garden maintenance practices.  A ‘good’ pruning plan is the selective removal of branches without changing the plant’s natural appearance or habit of growth — or, in extreme cases, bring the plant back to the plant’s natural appearance or habit of growth.  Shrubs trimmed into unnatural shapes or sizes for the particular species require more pruning than shrubs pruned to keep their natural shape (think of topiaries and boxwood hedges in a formal English garden).

Another thing to keep in mind is that you should be pruning to improve the health of the shrub by cutting out dead, diseased, broken, or overgrown branches that interfere with new growth.  You want to prune to control the shrub’s size, shape, flower, fruit and colored twig effect.

As you have both deciduous and evergreens, let’s break them down into their respective groups.

Deciduous:

The three methods used to prune a shrub hedge for a specific purpose are thinning out, renewal, and heading back or shearing.

By thinning out, a branch or twig is cut off at its point of origin from the parent stem, to a lateral side branch, to a “Y” of a branch junction, or at the ground level.  This method of pruning results in a more open plant and does not stimulate excessive new growth.  Considerable growth can be cut off without changing the plant’s natural appearance or habit of growth.  Plants can be maintained at a given height and spread for years by thinning out.  This method of pruning is best done with hand pruning shears, not hedge shears.  Thinning allows room for growth of side branches. Thin out the oldest and tallest stems first.

By renewal pruning, the oldest branches are gradually removed from an overgrown shrub at the ground level.  It is best to do this over a three-year or longer period, leaving the younger more vigorous branches.  New shoots that develop can be cut back to various lengths by the thinning method to develop into strong branches.

Heading back or shearing refers to cutting back a branch anywhere along the length of a stem.  The cut may be above a bud, below a bud, or it may even leave a stub.  The effect of heading back or shearing is to concentrate vigorous upright new growth below the cut.  This method of pruning is frequently done with hedge shears without regard for the natural form or branching of the plants.  If every branch or twig is headed back, more growth develops than was removed by the pruning.  The natural form of the plant is altered by the extra growth.  Hedges are pruned to a definite size or shape with hedge shears.

Avoid leaving stubs when pruning even a small shoot or twig.  Short stubs will not heal over properly and will eventually provide a source of entry for insects and diseases.  Cuts too far above a bud may destroy the bud by decay or die-back.  Cuts too close to the bud may dry out the bud, especially in winter.  The proper pruning cut should be 1/8 to 3/8 of an inch above the bud, slightly slanted away from the bud.

So when is the best time to prune your hedges?  It is ideal to prune most plants is during the dormant season prior to the start of new growth. Flowering shrubs may be an exception.  Shrubs that bloom in spring (i.e. lilac, forsythia, dogwood, etc.) may be pruned after flowering.  Late flowering shrubs that bloom on wood produced the same year can be pruned before growth starts in the spring.

Some landscape horticulturists believe the effect of the shrub’s structural branching characteristics is more important than its flowering effect in the total landscape design.  Therefore, it may be better to prune all flowering shrubs in early spring before new growth starts.  Some bloom will be sacrificed by this method.  As a botanically-trained horticulturist, I disagree with this; however, either method is recommended depending on this homeowner’s personal preference. One has to determine for himself the time to prune deciduous shrubs.

The tools I recommend for the job are:

~Pruning shears — for branches 1/2 to 3/4 inches in diameter. Twisting shears to cut larger branches will strain and weaken them. The anvil-type of pruning shears is satisfactory for general pruning. However, the scissors or draw-cut type hand shear is preferred for close-cut precision pruning.

~Lopping shears — have long handles and are designed to cut larger branches 3/4 to 2 inches in diameter.

~Pruning saws — have narrow blades, coarse teeth and are designed to cut on the pull stroke. Small curved pruning saws are useful to prune larger shrubs.

~Hedge shears — are used for shearing hedges or formal-shaped plants. Avoid using hedge shears for other pruning purposes.

Evergreens:

Pruning is an important maintenance practice for some evergreens. However, pruning can be kept to a minimum by the wise use and proper placement of plant materials in the landscape design. Evergreen plants can be divided into two broad categories: (1) Narrowleaf (needled) evergreens such as pines, junipers and yews; (2) Broadleaf evergreens such as rhododendrons, hollies and box. The narrowleaf evergreens are generally grow more rapidly than broadleaf evegreens, include many tree forms and are commonly grown for their foliage only. Broadleaf evergreens include many shrub forms and are often grown for their flowers and fruit as well as for their foliage.

Why Prune?

Limit the pruning of most evergreens to the removal of dead, diseased and mechanically injured wood and to the maintenance of the natural shape of the plants. Formal effects such as clipped hedges, topiary and espaliers require regular attention and special equipment.

When to Prune:

Dead, diseased and broken wood can be removed at any time of year. The best time for general pruning is in late winter or early spring, immediately before growth resumes. Narrowleaf evergreens may be pruned a second time in June before the new growth has matured. It may be necessary to give particularly fast-growing plants an additional light pruning or two during the growing season. Good judgment must be exercised when pruning flowering evergreens so as not to drastically reduce the amount of next season’s flowering woodÜany pruning should be done as soon after flowering as possible. Severe pruning can usually be avoided if pruning is done annually.

How to Prune:

It is important to have the necessary tools in proper working order for pruning your plants. These tools include a hand pruner, lopping shears, hedge shears and a curved pruning saw. Narrowleaf evergreens are characterized by growth that is either whorled or random (non-whorled). When pruning pines, make cuts just above the needle whorls. Most new lateral growth is stimulated at these points rather than along the stems between the whorls.

In pruning most other needled and broadleaf evergreens, cuts can be made at any point along the branch, but care should be taken not to cut too far back into the older wood, because new growth is not as readily produced from such wood. When selectively pruning, it is a good practice to cut the growth back to a side shoot. Some evergreen species withstand relatively heavy pruning. This is true of such plants as Japanese yew, box and evergreen privet. These plants can be sheared, which involves the uniform removal of new growth to make a plant conform to a prescribed shape. Because shearing encourages the formation of additional lateral growth, a more dense habit of growth is created. The amount and manner of pruning depend to a large extent on the type of plant, its location and the particular tastes of the homeowner.

Pruning Pointers for Specific Plants:

Pines
Prune in early spring. Make cuts just above needle whorls. Additional pruning may be done before new growth hardens in June. Pines normally require little pruning.

• Spruces & Firs
Cuts may be made at any point along the younger portions of the branches. The best time to prune spruces and firs is in the early spring. Pruning is necessary to maintain the natural shape of the plants.

•  Juniper, camaecyparis and arborvitae
This group consists of many tree, shrub and prostrate forms. These species can withstand relatively heavy pruning and many may be trained into various forms by shearing. Early spring pruning is best, but additional light pruning later in the season may be necessary.

•  Yew and hemlock
It is preferable to allow these plants to retain their natural form, but both respond well to heavy pruning and shearing. Yews are able to withstand exceptionally severe pruning into the older wood. Early spring is the best time for pruning, although occasional light pruning later in the season may be necessary.

• Rhododendron, azalea, pieris and mountain laurel These plants generally require very little pruning, as they are slow-growing. Old flower clusters should be removed immediately after flowering. Prune out only dead, diseased, weak or wayward branches.

• Box, evergreen privet, barberry and pyracantha
With the exception of box, these species grow rather rapidly. All these plants will stand heavy pruning, which is best done in early spring. Because they are generally quite vigorous, additional trimming during the growing season may be advisable.

•  Hollies
These plants include both tree and shrub forms. American holly may be pruned in December for Christmas greens. Chinese holly is also a source of attractive greens and may be trimmed in the early spring. When pruning American holly, always make the cut at a node, just above a lateral bud. Prune so as to maintain the natural shape of the tree. The shrubby Chinese and Japanese hollies can be more severely pruned and may require some additional light pruning during the growing season.

• Mahonia and leucothoe
These are rather slow-growing plants which require little annual pruning–if pruning is necessary, do it immediately after these plants flower in the spring.

 

© Mertie Mae Botanics LLC and Horticulture Talk!, 2013. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Mertie Mae Botanics LLC and Horticulture Talk! with appropriate and specific direction to the original content.

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