According to an old saying, if you’ve properly pruned your shrubs, they shouldn’t look pruned. That’s sage advice — unless, of course, you’re pruning shrubs to look like Donald Duck at Disney World.
Approach shrub pruning with confidence, because I’ve never encountered anyone yet who killed a deciduous (leafy) shrub by pruning improperly. There are definite guidelines to follow, though, that will make the resulting shrubs healthier and more appealing.
Shrubs are pruned for several reasons. Pruning reduces or maintains height and width, removes dead or broken branches, improves flowering, promotes healthy growth and can rejuvenate an overgrown shrub.
Quality pruning tools make the task easier, and higher-end tools are worth the extra investment and can last a lifetime. Three tools will handle most pruning: a hand-held pruning shears to cut branches pencil-size in diameter; a long-handled lopper for 1-inch-diameter branches; and a pruning saw for larger branches.
Hedge trimmers are needed only if you have a formally trimmed hedge, and they are not useful for general shrub pruning.
Most deciduous shrubs — those that lose leaves during winter — are best pruned in early spring before leaf buds begin to swell and open. However, for shrubs that bloom in spring, such as lilacs and forsythia, pruning should wait until after flowering, because earlier pruning would cut away the existing flower buds that will soon open.
Wait to prune evergreen shrubs until May and June. Most evergreens require little pruning, other than to maintain height or width, and they don’t tolerate extensive pruning the way deciduous shrubs do. Confine evergreen pruning to the outer areas with green foliage. If pruned back to interior branches bare of foliage, the blank stems do not produce new growth.
Pruning is not the same as shearing, which is like giving shrubs a rounded haircut. Shearing — using hedge clippers or trimmers — causes dense growth at the outer perimeter that shades the interior, making lower branches sparse and leggy. Shearing should be limited to formally trimmed row-type hedges. Individual shrubs in the landscape develop an unnatural, tight appearance if sheared with hedge trimmers.
Proper pruning, on the other hand, is a more selective approach, which maintains the natural form and appearance of each shrub. When properly done, shrubs will look neat, yet the pruning won’t be an obvious haircut.
Shrub pruning can be divided into two types: maintenance pruning and rejuvenation pruning. Maintenance pruning keeps shrubs at the preferred size, removes any dead branches, and promotes fresh branching, and it's best done yearly or every other year. Rejuvenation pruning takes an old, tangled, overgrown shrub and restores it to fresh growth with a fairly aggressive pruning approach.
Guidelines for maintenance-type pruning
Two basic pruning cuts are involved. “Heading back” means pruning branches back in size, reducing height or width. “Thinning out” means removing branches at their point of origin at ground level or attachment, to reduce clutter within a shrub.
To maintain size, with a hand-held shears or loppers, selectively cut back branches, staggering heights slightly to avoid a tightly sheared appearance. Cut back to a bud or side branch to avoid leaving empty stubs.
Remove dead or broken branches back to ground level.
Thin out clutter inside the shrub by cutting selected branches back to ground level or a side branch. Reducing interior branch clutter by at least a third allows the remaining branches to thrive or bloom more prolifically.
Maintenance pruning especially benefits shrubs like potentilla, spirea, ninebark and dogwood, done in early spring before leaf-out. Such pruning on spring-blooming shrubs like lilac and forsythia should wait until just after flowering.
Guidelines for rejuvenation-type pruning
Dogwood, lilac, forsythia, spirea, potentilla, viburnum, ninebark, euonymus and weigela are examples of shrubs that can be renovated if old and overgrown.
The best time to restore overgrown shrubs is in the early spring before new growth begins, including lilac and forsythia. The season’s flowers will be sacrificed, but the benefits outweigh the temporary loss.
To rejuvenate these shrub types, prune all branches down to 6 inches above ground level, in a total cutback. Within one growing season, these shrubs will look like fresh, new plantings again.
An alternative method involves pruning back a third of the branches over a three-year period, but I favor the total cutback method, which rejuvenates the shrub instantly, rather than stretching the process over multiple years.
Keep shrubs healthy in following years with maintenance pruning.
Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at firstname.lastname@example.org.