There are two types of hedges, formal and informal. The formal hedge is pruned or sheared to a definite size and shape one or more times each growing season. The informal hedge, often a row of shrubs planted close together but allowed to grow normally, is pruned annually to thin out the oldest wood and to maintain a desired height and width.

Starting a Formal Hedge:

After planting, small shrubs one to two years old should be cut back to about 6 to 10 inches above the ground. This will force new shoots near the ground to develop into a thick, bushy shrub. Delay in cutting back at planting, a fault of many gardeners, will result in a leggy, unsatisfactory hedge later.

Older shrubs used to start a hedge can be cut about one-third from the top. This helps develop a thick, bushy hedge of many twiggy stems. No additional pruning is needed on newly-planted hedges until the next spring.

Pruning Formal Hedges:

The most important step in starting a new hedge is the first shaping the next season after planting. A narrow pyramid or inverted "V" is the recommended shape. For example, a hedge 5 feet high should be 2 1/2 feet at the base and about 1 foot at the top to be in good proportion.

The top of the hedge should be trimmed slightly rounded or pointed. This allows sunlight to reach the lower branches. If the top becomes as wide or wider than the base, the lower portion is too shaded and produces thin weak growth. A taller hedge requires more attention to maintain proper shape and taper.

Hedges can be kept vigorous for years by annually thinning out a third to a fourth of the oldest branches with hand pruners or pruning saws. In addition to regular shearing, cut these branches back to the parent stem at the ground or to a lateral, or side, branch in the spring before growth starts.

Shrubs with red or bright-colored winter bark can be kept colorful by cutting out one-third of the oldest stems each year or prune one-third of the oldest stems every three years.

Time to Prune:

Shrubs used for hedges, except evergreens, can be pruned almost anytime. Slow-growing hedges that require one annual pruning can be sheared after they have completed their season's growth in early to mid-June. Fast-growing hedges can be trimmed two or more times, in early June, mid- to late-July and early to mid-September.

Rejuvenation of Old Hedges:

Overgrown, neglected deciduous hedges can be restored to their former beauty by one or a combination of methods. Over a three-year period, before new growth starts in the spring, cut back all branches to a few inches above the ground, along with regular shearing. Another way is to cut back the top and sides of the hedge 8 or more inches inside of the desired height and width in early spring. Follow by shearing the new growth for a thick, twiggy effect.

Evergreen Hedges:

No pruning is needed after planting young evergreens three to five years old. For the first two years after planting, prune back only the terminals and laterals as needed to begin the desired shape and taper.

Pine and spruce should not be pruned beyond the current season's growth. These evergreens do not produce new buds or growth from older branches, but from buds already formed. Prune these conifers to remove only a part of the new growth.

Pine hedges can be trimmed with hand pruners or a knife for best effect. Hedge shears will result in mutilated needles with brown buds and give the hedge an unsightly appearance. One-half to two-thirds of the early spring candle-like new growth can be pinched by hand or cut off before the needles unfold. More pruning can be done again in late June or early July before the new growth hardens.

Spruce produce new growth only once a year from existing buds. Spruce hedges can be sheared in early spring before this new growth develops from the existing buds. The new shoots can be sheared again in late spring to early summer, if desired.

Other evergreens such as taxus (yew), juniper, arborvitae and hemlock make good hedges. They seldom require more than one pruning in early spring and again in mid-July, if desired.

Pruning Tools:

Hedge shears are best used to prune formal hedges. Pruning shears are used for branches 1/2 to 3/4 inches in diameter. Lopping shears have long handles, cutting larger branches 3/4 to 2 inches in diameter. Pruning saws have narrow blades and coarse teeth and are designed to cut on the pull stroke. Small curved pruning saws are useful to prune larger shrubs.

Adapted from Fred K. Buscher, Ohio State University Extension, 2000