Pruning is both an art and a science. No garden practice is less understood than pruning. Most gardeners recognize the need for pruning, but most are hesitant to start. There are no simple steps to follow for becoming an expert pruner, but knowing how a plant grows and the reasons for pruning should help.
If a plant has any dead wood, such dead wood should obviously be removed. This improves the appearance of the plant and lessens the chances of decay. Narrow-angled crotches are weak crotches that are likely to split as the tree or shrub matures. Wide-angled branches are strong branches. In pruning, leave wide-angled branches whenever possible and remove narrow-angled branches. Lower tree branches that interfere with traffic around the yard should be removed as soon as they start to interfere. Trees that are very dense exclude light from the lawn and should be thinned to permit light to filter through. Occasionally the leader (main stem) of a tree, like a spruce, is injured. Several lateral branches usually grow upward to replace the leader. Allowing these to grow results in a multiple-stemmed tree. All but one of these leaders should be removed or cut back as soon as possible. Sometimes trees and shrubs are planted in limited spaces. Such plants must be pruned to limit their size. Flowering and fruiting are better on relatively young branches. Fruit trees that have not been pruned may become overly reproductive. Because too many fruits set for the limited vegetative growth, they do not receive an adequate supply of the nutrients needed to develop fruit size and quality. Pruning to stimulate vegetative growth would improve the size and quality of the fruit. The same rationale for pruning applies to flowering shrubs. Removing some of the older stems favors the development of young, vigorous growth and thus improves the size and quality of bloom.
To do a proper job of pruning, it is important to purchase tools of high quality. They cost more but last longer and enable you to do an excellent job of pruning. Hand pruning shears are of two general types: the anvil with a single cutting blade that cuts against a flat plate and the shearing type with two cutting blades. The shearing type is best for woody plants. If pruning is done regularly most of it can be accomplished with a pair of good hand shears. The long-handled shears, or loppers, are good for larger branches up to I inch or more in diameter. A pruning saw is needed for removing larger branches and for renewal pruning of large shrubs (see discussion under How to Prune on p. 56). Many types of pruning saws are on the market. A saw with a blade that can be adjusted to get between crowded branches is useful. The type of pruning saw styled after the hacksaw but with coarser teeth is excellent for pruning. Avoid the type that has teeth on top and bottom.
The proper time for pruning depends on a number of factors like time of bloom, disease problems, and sap flow. Most shade and fruit trees are best pruned during late winter. Exceptions are trees that bleed, such as maples and birch, which should be pruned after the leaves have fully opened.
Shrubs that flower on new wood, like hydrangeas and summer-flowering spireas, should be pruned before growth starts in the spring. Prune spring-flowering shrubs as soon as the flowers have faded.
Trees and shrubs that have a disease like fire blight or oak wilt should not be pruned during the growing season. It is best to prune such trees when the temperature is below freezing to avoid spreading the disease. Hedges should be pruned several times during the growing season whenever new growth is sufficiently long. Evergreens like pines and spruce are best pruned when new growth develops in the spring. Junipers, arborvitae, and yews can be pruned anytime.
Knowing how to prune is something that one learns by experience and study. Each plant has a different habit of growth and requires special pruning. In general we practice two kinds of pruning: tip pruning and renewal pruning.
In tip pruning, the terminal growth is removed. The terminal bud has apical dominance: it synthesizes a growth-regulator substance which diffuses downward to inhibit the growth of lateral buds. By removing the terminal growth, the inhibiting effect is removed and lateral buds develop. Such pruning results in a dense plant. Formal hedges are pruned in this manner. We also practice tip pruning when we pinch back the new growth on chrysanthemums in the spring. Evergreens that must be grown in a limited space are often tip pruned. Tip pruning results in an unnaturally formed plant and should be practiced only where a formal effect is desired or where space is limited.
Renewal pruning involves removing entire stems or branches. It is a thinning-out type of pruning. For most flowering shrubs the best blooms occur on stems that are from 2 to 4 years old. On very old stems the flowers are small and overcrowded. By removing the oldest stems each year, the plant retains the maximum amount of high-quality flowering wood. Removing the old stems causes vigorous new growth to develop from the base of the plant.
Such pruning retains the natural form of the plant and keeps the plant young and productive. Renewal pruning is also practiced on fruit trees to encourage new growth and to let sunlight enter the trees.
Several things must be kept in mind when pruning. In pruning back a stem, use sharp pruning shears and make the cut about lA inch beyond a bud and parallel to it. In removing a branch, make a clean cut close to the main stem. Never leave a stub. In removing a large branch, undercut about 1 foot from the stem and then cut from above to remove the weight of the branch. Next make a cut close to the stem, holding onto the stub as you remove it to prevent the tearing of the bark.
Wound dressings are often recommended on cuts that are more than 2 inches in diameter. The value of wound dressings is somewhat questionable. Wounds seem to heal about as quickly whether they are treated or not. Wound dressings like Tree-Cote, orange shellac, and grafting wax are often used. Avoid using a paint containing lead.
Hedges may be either informal or formal. The informal hedge receives little or no pruning. The formal hedge is sheared using the tip-pruning method. Hand or electric hedge shears are used for shaping the hedge. The pruning should start at planting time. The newly planted hedge should be pruned back to within about 6 inches of the ground. This will result in lateral branching close to the ground. When new growth is about 6 inches long, the hedge should be pruned. It may be necessary to prune 2 or 3 times during the season. In pruning a formal hedge, the sides should gradually taper inward toward the top. The top may be flat, rounded, or pointed. The important thing is to have the base broader than the top so that light can reach the base of the hedge.
Hedges are often trained to a shape that is the reverse of this ideal. The "umbrella" effect is achieved by not pruning at planting time and by pruning only the top. The result is a hedge that is open and narrow at the base, with a broad, flat top.
Formal hedges require much work, and similar results can be achieved by selecting the right plants to grow as an informal hedge.
Espalier pruning involves training a tree or shrub in one vertical plane. Such plants are usually trained against a wall. Pruning must start when the plant is young and must be continued throughout its life. All the branches are removed except those that can be trained to grow in the one vertical plane that parallels the wall. To provide support, it is usually necessary to fasten the main branches to the wall. In Europe espaliered fruit trees are often grown on the south side of a wall to capture as much sunlight and warmth as possible to mature the fruits.
Pruning is often done to achieve certain artistic effects. Yews are often pruned into shapes resembling animals like ducks and rabbits. This can be a fascinating hobby but it does little to enhance the beauty of the plants.
Certain herbaceous plants benefit from pruning. A tall, leggy coleus or geranium plant can be made full and rounded by pruning the tip of the stem, thus removing the apical dominance and forcing lateral buds to develop. By pinching the tips of the stems on a chrysanthemum plant in the spring, lateral branches form. This produces a fuller plant with more flowering stems. Larger blooms are produced on peonies and dahlias if lateral buds are removed. Tomato plants are often tied to stakes. This requires that lateral branches be removed as they form.
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