Most hedges are formal; they are sheared into flat-sided shapes to form low or tall walls. Such hedges, which serve as living fences or privacy screens in small spaces, look neat if kept regularly trimmed.
Informal hedges, maintained with loppers or hand pruners, have a looser, more natural shape than formal hedges. It may seem to be more work to prune an informal hedge compared to shearing a formal one, but it really isn’t because the informal hedge needs to be pruned less often. Expect to dedicate more space to an informal hedge to accommodate the looser form.
Pruning a Formal Hedge
Properly pruned, a formal hedge is a wall of green, dense and flat. Its top and sides are smooth and its corners are sharp. You may shape it as you would shape any wall, but the base should always be wider than the top so that enough light reaches the base to keep it green. This is especially important on those parts of the hedge that get less than full sun, such as the north side of the hedge, or parts that are partially shaded by a tree or building. If the base is shaded by the top, branches will die, leaving holes that grow and merge until the base is devoid of foliage.
A formal hedge is an empty shell of foliage, only a few inches thick. The density of the exterior foliage keeps light from reaching the interior. The interior foliage disappears, leaving leafless branches and twigs. This shell of foliage needs constant renewal. It is renewed by allowing it to grow just a little bit with each pruning.
To allow this growth, decide on a minimum and a maximum size for the hedge. For example, the minimum size for a hedge to give you privacy might be high enough that passers-by can’t see over it. The maximum size might be high enough that it begins to feel oppressive. Follow the planting and training directions in Planting Hedges until it reaches the minimum size you’ve selected. Once it reaches that size, remove all but 1/4 inch of new growth with each shearing. This 1/4 inch allows the necessary renewal, keeping the shell of foliage fresh and healthy.
Shear hedges with hand or electric hedge shears. Stretch a line between temporary posts at each end of the hedge to help keep cuts straight. The top can be flat, slightly rounded, or pointed. The taller the hedge, the more attention must be paid to maintaining proper taper. If the top becomes as wide or wider than the base, it will shade the branches below and eventually kill them.
Shear whenever the hedge begins to look ragged. Slow-growing hedges may only need 2 or 3 shearings a year. Fast-growing hedges like privet may need several. How often you shear also depends on how important neatness is in your garden look. Garden styles that depend on crisp lines and flat planes need to be sheared more often to maintain that look.
Shear most conifers before growth begins in spring so that the flush of new growth covers the pruning cuts. The plant can also be sheared during or after the first growth spurt. Continue shaping evergreen hedges as needed, but stop early enough in the season for the new growth to mature and harden before freezing weather arrives. Keep the base wider and taper the sides to a narrower top. Follow the instructions for pruning deciduous formal hedges, with the following exceptions.
With conifers, at planting time cut back long leaders but otherwise do not prune them until two years after planting. Do not prune pine, spruce, or fir deeper than into the current season’s growth; few, if any, buds develop on older wood and recovery is limited. Arborvitae and false cypress resprout from old wood that still has foliage.
Prune pine hedges by cutting back new growth before it hardens. Use hand pruners to cut pines before the needles unfold; hedge shears will cause the needles to develop unattractive brown tips. Hedge shears can be used to prune spruce and fir hedges after the growth hardens in midsummer or before new growth begins in spring.
Yew and juniper, which have a longer growing season than other narrowleaf evergreens, often need pruning at least twice during the growing season to retain a neat, formal look. Prune these hedges just after the first flush of spring growth and then again after the second flush in midsummer. They can also be pruned in late summer but little regrowth will emerge to hide the cut stems. New growth arising from sheared shrubs such as yew and juniper is especially fast, thick, and vigorous. When sheared these shrubs increase in both height and spread each year; they may eventually outgrow their usefulness in the garden.
Rejuvenating an Oversized Hedge
After many years, the hedge will reach its maximum height, becoming too large to do the job you want it to do. At that point, cut it back to its minimum height and shape. This pruning will probably require lopping shears rather than hedge shears; you will be cutting some large branches. You will also cut off all the leaves, leaving only bare branches. Do this drastic cutting in the spring, just before new growth begins, so that the hedge recovers as quickly as possible. After regrowth begins, resume shearing as before.
Pine, spruce, fir, and other needled evergreens do not resprout if cut back severely. The only way to renew them is to cut back to a whorl of branches on a main or side stem; new growth will emerge from existing buds and remaining branches. By repeating this procedure for several years, it is possible to gradually lower the height and narrow the width.
Pruning an Informal Hedge
Prune an informal hedge with hand pruners rather than hedge shears. Keep its exterior dense and the size and shape desired with a single annual pruning, made just before spring growth begins. Using thinning cuts, reach into the hedge and cut long branches back to a side shoot. Follow the natural growth lines of the shrub if you wish, or prune it to a shape that pleases you. Thinning cuts keep the hedge the size and shape you want without making it as dense as a formal hedge. Light penetrates farther into the interior of the shrub, and leaves grow throughout it. Except for pines, which must be pruned before the new growth hardens, hedges can be thinned anytime.
Another type of informal hedge is one pruned frequently with hedge shears, as a formal hedge is, but sheared to a free-form shape. Usually this method produces a billowy, rounded look with a whimsical air.