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.
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.
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.
evergreen plant with broad leaves that are not needle-shaped.
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.
Deciduous and Flower Shrubs
Pruning recommendations for most deciduous shrubs consist of thinning out, gradual renewal and rejuvenation pruning. In thinning out, a branch or twig is cut off at its point of origin from either the parent stem or ground level (Figure 8). This pruning method results in a more open plant; it does not stimulate excessive new growth, but does allow room for growth of side branches. Considerable growth can be cut off without changing the plant's natural appearance or growth habit . Plants can be maintained at a given height and width for years by thinning out. This method is best done with hand pruning shears, loppers or a saw, but not with hedge shears. Thin out the oldest and tallest stems first.
In gradual renewal pruning, a few of the oldest and tallest branches are removed at or slightly above ground level on an annual basis (Figure 8). Some thinning may be necessary to shorten long branches or maintain a symmetrical shape.
To rejuvenate an old, overgrown shrub, remove one-third of the oldest, tallest branches at or slightly above ground level before new growth starts.
The general pruning procedure shown for crape myrtle (Figure 9, applies to many large shrubs and small tree species. If a shrub is grown for its flowers, time the pruning to minimize disruption of blooming. Spring flowering shrubs bloom on last season's growth and should be pruned soon after they bloom. This allows for vigorous summertime growth and results in plenty of flower buds the following year.
Some examples of shrubs that bloom on last seasonís growth are: Japanese Quince, All forsythia, honeysuckle, hawthorne, azaleas and rhododendrons, shrub roses, white spireas and viburnums
Some shrubs that bloom after June usually do so from buds, which are
formed on shoots that grow the same spring. These shrubs should be pruned in later winter to promote vigorous shoot growth in spring. Examples of shrubs that bloom on current season's growth include:
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.
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.
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.Pruning groundcover usually is necessary only to remove unhealthy tissue or to promote spreading. Vigorous groundcovers include honeysuckle, winter creeper, Asian jasmine, Vinca minor, Vinca major and English ivy. These groundcovers may be mowed with a rotary lawn mower or cut back to 4 to 6 inches in height every few years to keep them vigorous, neat and well manicured. The best time to do this is in the early spring after danger of frost has passed but before the new growth starts.