By Dr. Douglas F. Welsh, Professor and Extension Horticulturist
Texas A&M University
A well-shaped hedge is no accident. It must be trained from the beginning. The establishment of a deciduous hedge begins with the selection of nursery stock. Choose young trees or shrubs 1 to 2 feet high, preferably multiple-stemmed. Cut the plants back to 6 or 8 inches when planting; this induces low branching. Late in the first season or before bud-break in the next season, prune off half of the new growth. In 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 the plants to grow untrimmed to the final height before shaping; 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 o slightly pointed top and with sides slanting to a wide bas (fig. 1).
After plants have been initially pruned to induce low branching, the low branching is maintained by trimming the top narrower than the bottom so that sunlight can reach all of the plant leaves (Fig. 2).
These questions often arise and the answers depend to some extent on how formal an appearance is desired. How often should this hedge be trimmed? When should I trim? 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 the desired height. Then carefully trim for the next few years to give it the desired shape and fullness. Hedge plants may occasionally decline too much to recover from this treatment, thus making it necessary to replace them.
Rejuvenating evergreen hedges is more difficult. As a rule, evergreens cannot stand the severe pruning described. 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-around tool. It will cut much better an 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 are 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.
This material originally appeared in the 'Master Gardener Handbook'.
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