Pruning Shrubs

Know When to Prune: Most shrubs can only be pruned at certain times of year, usually when they're dormant. Shrubs that flower in the spring should only be pruned after the flowers fade, while shrubs that flower later in the summer should only be pruned in early spring.

Before pruning a shrub, you also first decide what you want your cuts to accomplish. As with trees, you should remove any dead or crossing branches. And most shrubs do require occasional thinning, especially the older ones. When you thin a shrub, you remove the oldest branches right down to the ground. That opens the center of the shrub to sunlight, encouraging new branch growth and increased leaf production throughout the shrub. The key is to remove those branches totally. Many homeowners never really thin their shrubs, relying instead on periodic shearing of the branch end. That encourages heavy leaf production at the branch ends, which prevents adequate leaf production inside the shrub and results in leggy shrubs with long bare stems and dense surface growth.

Follow Proper Pruning Techniques

Pruning, like any other skill, requires knowing what you are doing to achieve success. The old idea that anyone with a chain saw or a pruning saw can be a landscape pruner is far from the truth. More trees are killed or ruined each year from improper pruning than by pests. Remember that pruning is the removal or reduction of certain plant parts that are not required, that are no longer effective, or that are of no use to the plant. It is done to supply additional energy for the development of flowers, fruits, and limbs that remain on the plant. Pruning, which has several definitions, essentially involves removing plant parts to improve the health, landscape effect, or value of the plant. Once the objectives are determined and a few basic principles understood, pruning primarily is a matter of common sense.

The necessity for pruning can be reduced or eliminated by selecting the proper plant for the location. Plants that might grow too large for the site, are not entirely hardy, or become unsightly with age should be used wisely and kept to a minimum in the landscape plan. Advances in plant breeding and selection in the nursery industry provide a wide assortment of plants requiring little or no pruning. However, even the most suitable landscape plants often require some pruning. The guidelines presented in this publication should be helpful when pruning any plant.

Reasons for Pruning

1.  To train the plant

2. To maintain plant health

3. To improve quality of flowers, fruit, foliage or stems

4. To restrict growth

Plan Approach to Pruning

Pruning should follow a definite plan. Consider the reason or purpose before cutting begins.

By making the pruning cuts in a certain order, the total number of cuts is reduced greatly. The skilled pruner first removes all dead, broken, diseased or problem limbs by cutting them at the point of origin or back to a strong lateral branch or shoot. Often, removing this material opens the canopy sufficiently so that no further pruning is necessary.

The next step in pruning is to make any training cuts needed. By cutting back lateral branches, the tree or shrub is trained to develop a desired shape, to fill in an open area caused by storm or wind damage or to keep it in bounds to fit a given area. To properly train a plant, one should understand its natural growth habit. Always avoid destroying the natural shape or growth habit when pruning unless maintaining a close watch over the plant, for after a period of time it attempts to assume the more natural growth habit.

Make additional corrective prunings to eliminate weak or narrow crotches and remove the less desirable central leader where double leaders occur. After these cuts have been made, stand back and take a look at your work. Are there any other corrective pruning cuts necessary? If the amount of wood removed is considerable, further pruning may need to be delayed a year or so. Remove water sprouts unless needed to fill a hole or to shade a large limb until other branches develop.

Definitions of Terms

Broad-leaved evergreen---an evergreen plant with broad leaves that are not needle-shaped.
Caliper---refers to the diameter of a tree. In nursery-landscape practice, caliper is measured 6 inches above the ground level up to and including 4-inch diameter size and 12 inches above the ground level for larger sizes.
Candle---refers to early spring growth of pine shoots before needle expansion.
Central leader---the main stem of the tree from which other branches develop. In most cases, it is the trunk.
Crotch---the angle developed between two connecting branches.
Deciduous---plants that normally have leaves only during the growing season and lose their leaves during the dormant season.
Dieback---the dying back of stems due to adverse weather conditions, insects, diseases or other causes.
Dormant---the period of the year when a plant is not growing.
Espalier---to train a plant on a wire or trellis against a wall or other support.
Lateral---a branch originating from the main trunk.
Multiple stemmed plants---plants with more than one stem form the base compared to plants with only a central leader.
Narrow-leaved evergreen---an evergreen plant with leaves that are needle-shaped.
Permanent branch---a branch that is part of the major growth habit of the tree, usually originating from the trunk.
Radial branch spacing---the distribution of branches around the trunk of a tree.
Scaffold branching---a permanent branch originating from the trunk and becoming a part of the major branching or framework of the tree.
Shearing---cutting back plants with hedge shears resulting in a very formal growth habit. Limit shearing to hedges, topiary or where a formal garden is to be maintained.
Sucker---a vigorous shoot originating from root or stem tissue below ground.
Temporary branch---a branch usually originating from the trunk that is removed by pruning after permanent branches have been selected.
Terminal---tip ends of branches.
Thinning---removal of connecting branches to point of origin or shortening the length of a branch by cutting to a lateral.
Training---to dictate the development and growth of a plant by physical means, such as pruning.
Vertical branch spacing---distribution of branches up and down the trunk of a tree.
Water sprout---vigorous shoot arising from the trunk or older branches.
Wound---area where the bark of a plant is cut or damaged.
Wound dressing--- a specially formulated material often called pruning paint, which is applied to tree wounds.

Renewal Pruning

When shrubs are left to their own devices, the oldest branches and stems will actually turn woody, and that's not good because woody branches do not produce as many leaves and they start to look like trees.  You can put your fastest-growing shrubs on a 3-year renewal cycle so that the stems and branches are never more than 3 years old!

With slow-growing shrubs, the 3-year cycle would probably mean death, but a 5-year renewal cycle (taking out the oldest fifth of a shrub's growth every year) should work for most of them. 

Pruning Narrow-Leaved Evergreens

Since narrow-leaved evergreens produce new growth in spring and fall and do not grow much in summer, prune the first or second week in April in warmer sections of Texas and the first or second week of May or June in cooler areas. The only exception to this rule is pines, which should be pruned before the candle growth develops in the spring.

Prune evergreens according to their growth habits. Allow these plants to assume their natural shape. Pruning is a matter of cutting the branches so that a more desirable plant is attained through compact, controlled growth. This requires pruning individual stems rather than shearing. Shearing not only ruins the natural growth habit but prevents light from penetrating into the center of the plant resulting in foliage drop.

There are certain rules to follow for various types of narrow-leaved evergreens. Start pruning when evergreens are small, usually the first year after they come from the nursery. Then if they are pruned a little each year, severe pruning is not necessary. Remove dead branches whenever they occur. New foliage from surrounding branches will fill in these gaps. The spreading forms of junipers should have the tip ends of their growth trimmed each year. This holds the plants in check and induces a compact growth habit. An example of a vigorous-growing, spreading evergreen is pfitzer juniper. It is common for this plant to grow 12 to 18 inches or more each year. To maintain the natural shape of this plant, it is necessary to cut back to growing points. It also may be necessary to cut back into the previous year's wood to maintain the plant's size and shape.

For the narrow-leaved, upright evergreens, such as pines or junipers, little pruning is required. When pruning any narrow-leaved evergreen do not cut into bare wood behind the foliage on the tips. Since few adventitious buds are formed on older twigs, the plants may be damaged beyond repair. Do not cut the central leader of these plants except to remove a multiple leader. This may occur when the plants are young. Remove all but one of the stems, leaving the straightest and strongest. When pines are young and growing vigorously, the top growing point may outdistance the rest of the plant, resulting in an open space between the main body of the plant and the growing tip. To encourage the plant to branch and be more compact, cut the top back to a dormant bud located near the main body of the plant. If this cutting back is done when the plants are young, there is little effect on plant appearance. It is better to select a compact or dwarf form of narrow-leaved evergreen than to do a lot of pruning. Many narrow-leaved evergreens will have much of the inner foliage turn brown in the fall, which is the natural pruning process. The amount of browning may vary considerably from season to season. This is a natural shedding of older leaves and is comparable to the dropping of leaves by deciduous plants. This occurs principally on cypress and some pines. Extensive periods of hot, dry weather also contributes to the loss of leaves on narrow-leaved evergreens.

Pruning Broad-Leaved Evergreens

Broad-leaved evergreens such as gardenias, camellias, azaleas, pyracantha, hollies and photenias require very little pruning. Lightly thin broad-leaved evergreens grown for their showy fruit such as pyracantha and holly during the dormant season if needed for shaping. Remove old or weak stems. This group can go several years without pruning except for some slight cosmetic pruning to keep them neat. If too much wood is removed from these plants at anytime, summer or winter, the amount of fruit is reduced the following season. When these plants become old and straggly, cut them back 6 to 8 inches from the ground before spring growth begins. Don't cut them back too early, however, because a flush of growth could freeze and set them back. Prune only after the danger of the last killing frost is past. Such pruning stimulates the growth of new shoots from the base of the plant. Many gardeners prefer to remove only about one-third of the branches at one time and retain the general contour of the plant. This method also can be used. In the long run, probably the best thing to do with overgrown broad-leaved evergreens is to remove and replace them.

Pruning Formal Hedges

To turn a row of unruly shrubs into a formal hedge will probably require a couple seasons and several sessions of pruning, but here are the general steps:

At some point, you can determine the final size and shape of the hedge and then focus your pruning on keeping it that way.

Hedges are a row of plants that merge into a solid linear mass. They have served gardeners for centuries as screens, fences, walls and edging.

A well-shaped hedge is no accident. It must be trained from the beginning. Establishing a deciduous hedge begins with selection of nursery stock. Choose young trees or shrubs 1 to 2 feet high, preferably multiple-stemmed. When planting, cut the plants back to 6 or 8 inches; this induces low branching. Late in the first season or before bud-break in the next season, prune off half of the new growth. The following year, again trim off half.

In the third year, start shaping. Trim to the desired shape before the hedge grows to its desired size. Never allow plants to grow untrimmed to the final height before shearing; by that time, it is too late to get maximum branching at the base. Do not allow lower branches to be shaded out. After the hedge has reached the desired dimensions, trim closely in order to keep the hedge within chosen bounds.

Evergreen nursery stock for hedging need not be as small as deciduous material and should not be cut back when planted. Trim lightly after a year or two. Start shaping as the individual plants merge into a continuous hedge. Do not trim too closely because many needle-bearing evergreens do not easily generate new growth from old wood.

Hedges are often shaped with flat tops and vertical sides; however, this unnatural shape is seldom successful. As far as the plant is concerned, the best shape is a natural form, with a rounded or slightly pointed top and with sides slanting to a wide base (Figure10).

After plants have been initially pruned to include low branching, maintain by trimming the top narrower than the bottom so that sunlight can reach all of the plant leaves (Figure 11).

These questions often arise: How often should a hedge be trimmed? When should I trim? Answers depend to some extent on how formal an appearance is desired. In general, trim before the growth exceeds 1 foot. Hedges of slow-growing plants such as boxwood need to be trimmed sooner. Excessive untrimmed growth will kill lower leaves and will also pull the hedge out of shape. Trimming frequency depends on the kind of shrub, the season and desired neatness.

What can be done with a large, overgrown, bare-bottomed and misshapen hedge? If it is deciduous, the answer is fairly simple. In spring before leaves appear, prune to 1 foot below desired height. Then carefully trim for the next few years to give it the desired shape and fullness. Occasionally, hedge plants may have declined too much to recover from this treatment, making it necessary to replace them.

Rejuvenating evergreen hedges is more difficult. As a rule, evergreens cannot stand the severe pruning described above. Arborvitae and yew are exceptions. Other evergreen hedges may have to be replaced.

Tools

What tools should be used to trim hedges? The traditional pair of scissor-action hedge shears is still the best all-round tool. It cuts much better and closer than electric trimmers, which often break and tear twigs. Hand shears can be used on any type of hedge, while electric trimmers do poorly on large-leaved and wiry-twigged varieties, and sometimes jam on thick twigs. Hand shears are also quieter, safer and less likely to gouge the hedge or harm the operator.

Hand pruners are useful in removing a few stray branches and are essential if an informal look is desired. Large, individual branches can be removed with loppers or a pruning saw. Chain saws are not recommended for use on hedges.

Pruning Vines, Groundcovers

The problems with pruning vary with the different uses of vines. Vines left unpruned for many years become unattractive. They harbor wasps, collect trash and loose their landscape effectiveness. Prune them to prevent such hazards. Vines usually cover an arbor or wall. Used in these ways, they are easily pruned to give a clean, well-kept appearance for displaying flowers or fruit. Some vines, such as honeysuckle and winter creepers, grow so fast and thick that considerable pruning may be necessary while other species need little pruning. Prune most vines in Texas during the dormant season from February to May. Prune dead, diseased or damaged vines back to healthy wood. Cut interfering branches of woody vines such as trumpet creepers or wisteria back below the point of interference or at the junction with the main stem. Prune out the top one-third of overgrown or elongated stems. Prune old mature stems that are declining in vigor by one-third or more.

Each year, prune stems of trumpet creepers and wisteria to promote new growth and flowers. Prune back the top of the plant to force out new branches. Give special attention to wisteria because considerable confusion exists about pruning and flowering. Pruning wisteria extensively during dormant season encourages rampant vegetative growth the next spring. Instead, in July prune out the long, straggly growth leaving those branches needed for climbing. This is more likely to induce flowering than anything else. Cut shoots back one-third to one-half their length, which includes the production of short spurs upon which next season's flower clusters are borne. Wisterias bloom abundantly if planted in well-drained soil and full sun, watered well the first growing season and pruned in the summer.

Espalier plants are trained in patterns on a flat surface such as a fence or wall. With proper care, plants can be trained into almost any desired plant. Usually, one is willing to maintain such training indefinitely, however, it is best not to develop such a plant. Usually, it's easier to start with a trained plant purchased from a nurserymen. If a trained plant is not available, use a 1-year old plant. Most espaliers require pruning throughout the growing season to maintain the desired shape. In most cases, it's better to have some type of a guide or wire on the wall to encourage the plant to move in that direction.