This article is being written as a supplement to "Pruning Facts and Fiction". Pruning procedures for specific types of plants will be outlined. The plant categories covered are: Deciduous Shrubs and Trees; Evergreen Shrubs and Trees; Newly Transplanted Trees; Large Trees; Old, Overgrown Shrubs; and Hedges, Espaliers, and Topiary. I have not included roses in this article because their pruning requirements are so specific that I will be discussing them in yet another article, "Rose Pruning 101".
First, let's start off with a basic review of some general pruning procedures:
Always allow a shrub or tree to develop its natural shape, except when special effects are desirable, such as for hedges. �Haircut� pruning should be avoided. Instead, use the thinning technique on both shrubs and trees. Cut the branches at different lengths, 1/4" above an active bud. Remove twigs or branches selec-tively and thus reduce overcrowding. Some stems should also be removed at ground level. The length of new shoots should be reduced 1/3 to 1/2 of their length, which induces side shoots to develop.
Cutting above a bud prevents dieback of the stem and encourages a new branch to develop from the bud. The haircut technique causes a dense growth at the ends of the pruned branches which shades the rest of the plant, thus causing the plant to eventually develop a leggy appearance. If a shrub develops a weak, dense growth, thin out many of the smaller branches and twigs. This promotes the vigorous growth of the remaining branches. Also remove branches which tend to rub against one another, opening wounds for the entrance of disease.
Always remove dead, damaged, or diseased branches and limbs from established plants as well as newly planted trees and shrubs. The plant should then develop new, stronger growth, free of diseases. Also, remove dead flower branches, dead flowers, and old fruit stocks as soon as the flowers have wilted or the fruit has dropped. This stimulates new growth and helps to make a stronger tree or shrub. It also encourages plants such as rhododendrons to produce more flower buds for next season.
With evergreen shrubs, avoid shearing to artificial shapes. If the evergreen plant has a soft, feathery appearance, do not cut it square or make a round shrub out of it. Prune using the thinning technique, thus keeping the natural shape of the evergreen. Remember, the non-green portion of needle-leaved evergreen branches does not normally put out new branches. Therefore do not cut branches back to the old wood. Reduce new growth annually, and when removing the larger branches for thinning, cut close to the main trunk, leaving no stubs. Heavy thinning is needed only every few years.
With certain evergreens such as yews ( Taxus), a new flush of growth will occur in the early fall. Head back these long shoots to keep the plants in shape. Broadleafed evergreen shrubs are pruned in the same manner as narrowleafed evergreens, by thinning and heading back. Light pruning every year is preferred, but heavy pruning every three years is acceptable. Rhododendron species benefit from removal of flower heads immediately after flowering. Most types, such as hollies, pyracantha, azaleas, and euonymus, can be cut back severely, but avoid cutting all the way to the ground. Holly trees may be pruned at Christmas time.
To thicken the new growth of coniferous trees such as pines, spruce, or fir, pinch out 1/2 of the candle (the new growth) when it is approximately 2" long in the spring. Do not use shears, since they damage the needles that are around the candle and cause the cut edges to turn brown. This gives the tree an unsightly appearance. Do not top or remove the central leader, if the natural growth habit of the tree is desired.
If the terminal of a pine or spruce has been lost, it is necessary to aid the plant in growing a new terminal shoot. Without assistance, a single terminal will probably not be re-established, and multiple leaders will result. To form a new terminal, bend one of the youngest lateral branches near the terminal into an upright position. Secure it to the dead terminal stub or insert a stake for rigidity. After a season, this branch will take over as a terminal shoot. Once this occurs, remove the stub or stake, and the plant will resume its characteristic growth habit.
In the digging process at transplanting time, bare root trees and shrubs suffer root damage as well as a loss of roots. To compensate for this loss of roots, the leaf area of the plant should be reduced by 1/3 to reduce water loss due to transpiration and evaporation. The natural form of newly planted trees and shrubs should be preserved by thinning. Remove branches and parts of branches by cutting at different lengths as previously described. When the tree is approximately 2 years old, establish good branch spacing. Branches should arise alternately from the main stem and be well-spaced radially. This will allow stronger limbs to develop. Select branches with the widest angles in the crotch. The wider this angle, the stronger the limb attachment. On most shade trees, the top-most growing point is critical in achieving a form typical of the species. This growing point is called the central leader, and there should be only one. It should not be cut.
Where tree limbs are near power lines, call the power company and ask them to remove them. Do not try to remove tree limbs from power lines yourself. Low-hanging branches may cause injury to individuals mowing the lawn or walking on the street. Also, branches sometimes rub against the house and roof. To remove the branches that are over 1" in diameter, use the double cut method. If the double cut method is not used, the branch will tear and splinter the trunk. This removes a large portion of the bark, causing a large wound which calluses with difficulty and may further result in permanent damage to the tree.
To double cut, first cut halfway on the underside of the limb (about one foot from the tree trunk). Then (several inches further out) make a second cut through on the upper part of the limb. When the branch is removed, there is no splintering of the main tree trunk. Then remove the stub by conventional methods, taking care not to cut into the collar.
Beware of rejuvenation techniques sometimes used on large old trees. Homeowners are sometimes �conned� into having the tops of old trees completely cut back, leaving only the stubs. These stubs eventually decay. Also, since the tree is in such a weakened condition, it may die prematurely. If you have large limbs that need to be removed, secure the professional services of an arborist. An arborist can drop work a tree, that is, lower the height, by removing limbs that are causing problems. When completed, the tree will still retain the beauty of its natural shape. Remember, a tree that has a trunk diameter of 20-24 inches may be worth up to $10,000 on a replacement value scale. Therefore, if you have a large, valuable tree, secure the services of a professional arborist.
Another aspect of pruning is the renewal of declining shrubs. In renewal pruning, remove one-third of the old, mature stems per season. These large, old branches are removed at the ground level. Leave the young vigorous branches. The water sprouts that develop should be cut back to different lengths and encouraged to develop into strong branches for the shrubs by the thinning process.
Lilac wood often is more than 3 years old before it flowers. Therefore, large, overgrown lilac bushes can gradually be cut back over a period of years, but do not remove all the old flowering wood until the new growth begins to flower. Then the bush will flower every year and will not have any barren years.
If it is essential to immediately reduce the size of a shrub, rejuvenation pruning is appropriate for some species (Butterfly Bush, Forsythia, Oakleaf Hydrangea, Privet, Honeysuckle, Spirea, Lilac) Cut back the entire top of the plant to the ground line. Many new shoots will grow from the base, and they will require thinning. As much as 3/4 of the new growth should be removed, depending on the species.
Some plants frequently suffer winter die back of all above-ground stems. These may be safely rejuvenation pruned to produce rapid new growth. These plants are considered to be usefully winter hardy. They can be used for landscaping purposes similar to an herbaceous perennial, even though severe rejuvenation pruning often is necessary.
Hedges, Espaliers, and Topiary
Plants are occasionally sheared to unnatural shapes. Hedges as barriers are the most common example. However, hedges are often improperly pruned, with the top trimmed flat and the sides sloped inward so that the base is more narrow than the top. This shades the lower portion of the hedge, preventing dense leaf growth. Thus, the plants become leggy, the hedge becomes straggly, and the screening function is not achieved. In proper hedge shearing, the top is shaped more narrow than the base. This means that light can penetrate to the lower portions of the plants, growth can be maintained, and a full appearance over the entire height of the hedge can be attained. This simple technique helps the hedge remain a satisfactory barrier for a long period of time.
Two other types of pruning plants to unusual shapes are espalier and topiary. Both originated in European gardens and are very time consuming. An attractive plant requires both dedicated effort and constant atten-tion. Not all landscape designs are appropriate for such plants, and in all cases, their use should be limited to focal points due to their highly unusual appearance.
Espaliering is the practice of training a tree or shrub to grow flat. Almost any tree or shrub can be trained flat by continually removing growing points that go in un-wanted directions. Allow the rest of the growing points to develop in their own way.
Before locating a plant next to your house for espaliering, place an iron or wooden support a few inches away from the house. This prevents any disfiguration of the wall and allows for plant support and easy plant removal at a future date.
Topiary is a shearing technique occasionally done on boxwood, juniper, pyracantha, yew, and privet. Part the branches to find a basic form. Remove limbs you don�t want. Wherever you want to form a clump, leave some branches and shear them to the outline you desire. Remove all twigs and leaves along branches between clumps. Each season new branches and leaves will tend to fill in the spaces between clumps.