Pruning Trees, Shrubs, and Vines
When To Prune
When to prune depends on several factors, notably the species being grown and the reason you are pruning. Pruning can actually stimulate growth. Pruning back a weak branch in late winter or early spring will often cause the new growth that replaces it to grow much faster. To slow growth down, prune in early summer. These are the two basic principles of pruning, but there are numerous exceptions.
Prune conifers differently.
There are two kinds of coniferous plants that require different types of pruning. The first are those that put out their entire year's new growth all at once, in late spring. This group includes pines, spruces, and firs. They can be pruned by removing up to two-thirds of the new growth while it is still fresh and pale green. Do not prune them back to old wood because they will not produce new shoots from those sections. Conifers that grow throughout the summer, such as yews, arborvitae, and junipers, are pruned once in early summer and again, if necessary, later in the season. They can also be pruned more heavily, down to old wood if necessary.
What To Prune
What to prune depends a great deal on the effect you want to create. There are major differences between the way to prune shrubs and the way to prune trees.
Except under rare circumstances, ornamental trees should be left to take their natural shape and appearance, resulting in little need for pruning. They are usually pruned only to remove damaged or diseased branches or ones that cross, rub together, or form an overly acute angle with the trunk.
Topping is not recommended.
Young trees should be pruned as little as possible at planting time because hormones released by leaf buds and newly emerging shoots stimulate the growth of new roots. Weak and damaged branches, however, can be removed. Once young trees are established, they can be pruned to remove weak growth and give them a better form. When the tree has attained a fair height, any lower branches that interfere with human movement can removed, preferably over a two- to three-year period.
One common pruning technique in tree pruning is topping, or heading. This is not recommended. Topping involves pruning back the large branches of deciduous trees in an indiscriminate fashion to change the tree's natural shape into that of a round ball. This causes all sorts of problems, including wounds that heal poorly, severe dieback, and increased danger of wind damage. It also destroys the tree's natural symmetry. The process must be repeated, since topped trees will grow back even more vigorously.
Different pruning techniques are used on shrubs, depending on the desired effect. Formal hedges, topiaries, and other closely clipped forms are sheared, which means all branches are clipped to the same length. Some shrubs that bloom on new wood are also sheared back annually to the base to encourage a maximum number of branches and thus more flowers. Subshrubs, which die back nearly to the ground anyway, should also be sheared back annually.
Shrubs that bloom on new wood can be sheared.
Spring-flowering shrubs should be thinned.
Vines should be treated like shrubs. Those blooming on old wood (spring bloomers) should be pruned back after blooming, and those blooming on new wood (summer or fall bloomers) should be pruned back in late winter or early spring. Vines grown for their foliage often produce overly exuberant growth and need to be pruned regularly. They can be pruned back any time except late summer or early fall; pruning at that time of year can result in new growth that doesn't harden properly.
Large branches require a pruning saw and should be removed back to the trunk or a main branch. Cut neatly down to the collar (the ring of growth where one branch joins the trunk or another branch) without wounding it. Do not leave a stub, or the healing process will be long. For major branches, use the 3-cut method. Do not apply tree paint to wounds. Always sterilize pruning tools by dipping them in rubbing alcohol or other disinfectant between cuts. In most cases, major pruning on a large tree should be left to a professional arborist.
Always plant formal hedges so the base is wider than the top.
Most pruning and training is done strictly on a utilitarian basis: just enough to produce a healthy, attractive tree, shrub, or vine. But pruning can also be artistic, actually changing the shape of the plant according to human whim. Which type of pruning you prefer depends on your tastes. If you enjoy experimenting, you might want to try some ornamental pruning techniques.
Hedging is the most common form of ornamental pruning. Shrubs or small trees, often evergreens, are planted closely together--only one to two feet apart -- forming a wall or screen.
Informal hedges, usually planted with flowering shrubs, are the easiest to maintain; thin occasionally so new, healthy growth is produced. Formal hedges are trimmed into geometric shapes and require frequent shearing, often up to four times a year (less for conifers). The base of the hedge should be wider than the top, or the lower branches will be shaded out and die.
Trees used for pollarding must be able to survive harsh pruning.
Pleaching is accomplished by weaving and pruning trees and shrubs to form an arched tunnel. Two rows are planted with a wide path between them. When the plants reach the desired height, the tops are bent and woven together. This technique is usually applied on large estates.
Pollarding involves severely cutting branches back to the same point each year, usually on a large tree, forming pom-pom growths on the ends of thick branches. This technique has never been popular in North America, although it is widespread in continental Europe. Trees to be used for pollarding should be chosen with care since few species can survive such harsh pruning for long periods.
Espalier involves pruning small trees and shrubs into a two-dimensional form, usually against a wall or trellis. It can be geometric or free-form. Espalier can be used to give a formal look to your garden or, by training trees and shrubs up a south wall, to allow tender plants to grow in a hostile climate. Firethorn and fruit trees are frequent subjects for espalier.
Use the espalier technique to give a more
formal look to a garden. Or, as an excuse to say espalier.
Small branches can be pruned with pruning shears. Cut back to just 1/4-inch above a healthy side bud, at a 45° angle.
Cut at a forty-five degree angle.
- Undercut the branch halfway through to prevent tearing.
- Cut from above, slightly beyond the first cut.
- Cut from above, parallel to the collar, to remove the stub.