How to prune hedges

A properly pruned hedge is healthier, longer-lived, and better looking than one where a homeowner simply dove in with a pair of loppers. The right pruning also helps hedges provide the denseness and privacy you expect, compared with the bare spots that often result from a subpar job.

Hedges come two basic ways: Formal and informal. Formal hedges typically bear small leaves and are sheared to a smooth and uniform surface to create a solid, usually geometric wall of green. Informal hedges are loose and more casual in appearance. They have larger leaves, are generally wider than a formal hedge of the same height, and are often chosen in part for their flowers and fruit.

Pruning formal hedges

Formal hedges require pruning to control their size and to create a shape. Handheld hedge shears are fine for smaller hedges. Electric trimmers are better for larger jobs, and gas-powered trimmers are best for the largest hedges where trimming is done far from a power outlet.

Regular pruning lets you keep normally tall plants, such as hemlock, at a much lower height without their growing into a row of trees. Most formal hedges need pruning at least once a year, while those with faster-growing plants or in regions with a longer growing season may need it twice per season. Before planting a formal hedge, consider the time and expense of maintaining one that grows taller than you can reach or requires frequent trimming.

When to prune

For slow-growing evergreen shrubs, such as arborvitae and yew, prune in late spring or early summer just as the new flush of growth begins to mature and harden. (A plant is slow growing if new spring growth is 5 inches or less.) Look for a change in color from lighter to darker green. New growth will cover pruning wounds and cover the hedge. Some plants will need a late summer touch-up on a few shoots to maintain their formal look. But avoid cutting into old wood in late summer so that new shoots mature in time for winter.

For fast-growers such as hemlock, prune after the spring flush of growth. Doing so slows growth and leaves a neatly shaped hedge for the longest period. If the hedge requires a second pruning, do it by late July so that new growth can mature and harden before frost.

Prune hedges of deciduous shrubs in late winter or early spring while they're dormant. Prune again in midsummer to maintain their formal appearance.

How to prune

Choose a shear type and blade length based on the size of your hedge. For smaller hedges (18 inches high and about a foot wide), use hand or electric hedge trimmers with smaller blades of about 13 inches long. For taller hedges, use shears or trimmers with blades 30 inches long or longer to extend your reach.

For new hedges, begin pruning in the second season, gradually stepping up the height several inches each year. The early pruning will force the plants to branch low to the ground and produce a mature hedge that is dense and full all the way down. Don't cut too deeply except when rejuvenating. Cut into leafy growth just enough to shape and maintain size. Cutting into interior branches looks bad and, if done after the flush of spring growth, may remain visible for months.

Slope the hedge so that it is broader at the base than the top to allow sunlight to reach the lower leaves. Especially for tall hedges, consider using a template. Allow any hedge to grow at least 1/2 to 1 inch per year so that new growth can keep plants healthy. Once a hedge has become too tall or wide, prune deciduous hedges in late winter and evergreens in midspring to remove at least 6 inches of growth.

Use hand shears to shape a small formal hedge and a power trimmer for larger hedges.

Common formal hedge plants

Arborvitae Platycladus and Thuja

A hardy evergreen 20 to 30 feet tall. Can use informally.
When to prune: Late spring.
Rejuvenation pruning: No.

Common boxwood (Buxus sempervirens)

A moderately hardy evergreen.
15 to 20 feet tall. Can also use informally.
When to prune: Late spring.
Rejuvenation pruning: Yes.

Canada hemlock (Tusga canadensis)

A hardy evergreen.
40 to 70 feet tall.
When to prune: Late spring, again in late July if needed.
Rejuvenation pruning: Yes.

Japanese boxwood (Buxus microphylla japonica)

A moderately hardy evergreen 4 to 6 feet tall. Can also use informally.
When to prune: Late spring.
Rejuvenation pruning: Yes.

Japanese yew (Taxus cuspidata)

A moderately hardy evergreen 30 to 50 feet tall.
When to prune: Late spring.
Rejuvenation pruning: No.

Myrtle (Myrtus communis)

A tender evergreen 8 to 10 feet tall. Can also use informally.
When to prune: Early spring.
Rejuvenation pruning: Yes.

Privet (Ligustrum obtusifolium)

A hardy deciduous plant 10 to 15 feet tall. Can also use informally.
When to prune: Early spring.
Rejuvenation pruning: Yes.

Pruning Informal Hedges

Prune informal hedges selectively with hand shears to maintain or accentuate the shrub's natural shape, to remove wayward branches, and to encourage flowering. Indeed, lilacs are among the many informal-hedge shrubs with showy flowers or berries.

To keep pruning to a minimum, choose shrubs that grow to roughly the size of the hedge you want. That often means choosing a dwarf species or cultivar of an otherwise larger plant.

When to prune

If flowers or berries aren't an issue, prune in early spring before growth begins. That allows new growth to cover any gaps or pruning wounds. Keep individual plants roughly equal in size and shape, shortening wayward shoots. To encourage flowers or fruit, prune according to the shrub's growth cycle. If flowers come in early spring, prune in late spring or after flowers fade. If flowers come in late spring or summer, prune in late winter or early spring.

How to prune

Remove or shorten individual branches or stems. Use bypass hand shears and make selective cuts, reaching into the hedge and cutting just above natural branching points.

Use hand shears to selectively prune an informal hedge. Prune shrubs with late spring or early summer flowers in early spring; prune shrubs that have early spring flowers after flowers fade.

Common informal hedge plants

Dwarf fothergilla (Fothergilla gardenii)

A hardy deciduous shrub that grows 4 to 5 feet tall.
When to prune: Late spring.
Rejuvenation pruning: No.

Dwarf winterberry (Ilex verticillata "Red Sprite")

A hardy deciduous shrub that grows 4 to 5 feet tall.
When to prune: Early spring.
Rejuvenation pruning: Yes.

English laurel (Prunus laurocerasus)

A moderately hardy evergreen that grows
25 to 30 feet tall.
When to prune: Late spring or early summer.
Rejuvenation pruning: No.,/p>

Firethorn (Pyracantha)

A moderately hardy evergreen that grows
8 to 10 feet tall.
When to prune: Late spring.
Rejuvenation pruning: No.

Flowering quince (Chaenomeles)

A hardy evergreen that grows
4 to 6 feet tall.
When to prune: Late spring.
Rejuvenation pruning: Yes.

Japanese holly (Ilex crenata "Convexa")

A moderately hardy evergreen that grows
6 to 8 feet tall.
When to prune: Late spring.
Rejuvenation pruning: Yes.

Lilac (Syringa vulgaris)

A hardy deciduous shrub that grows
7 to 12 feet tall.
When to prune: Late spring.
Rejuvenation pruning: Yes.

Rhododendron and azalea

Varies; usually a hardy evergreen that grows
4 to 15 feet tall.
When to prune: Late spring.
Rejuvenation pruning: Yes.

Roses

Varies; usually a moderately hardy evergreen
that grows 4 to 8 feet tall.
When to prune: Early spring.
Rejuvenation pruning: Yes.

Rejuvenating an old hedge

Pruning back to within inches from the ground can rejuvenate some hedge shrubs that grow too large or become leggy and leafless near the base. Do it in early spring, before growth begins. Also be sure plants are in good health to ensure that they'll grow back.

There are two ways to rejuvenate a hedge. Rejuvenating all at once saves time, but means the hedge will be gone for a season or until the shrub fills in again. Doing it over two to three years is less drastic and leaves only some gaps.

Rejuvenate leggy shrubs by cutting back to within a few inches above soil. Do it all at once or gradually by removing a few of the oldest stems to ground each year.