The objectives of pruning shrubs are to maintain vigor, remove damaged or diseased branches, help maintain the natural size and shape of a plant, and improve flowering and fruiting. There are four basic pruning techniques used for maintaining shrubs: heading back, renewal, rejuvenation, and shearing. For information on pruning specific shrubs, download the following list.
TIME TO PRUNE
A general rule-of-thumb is that shrubs that bear flower buds on the previous year’s growth should be pruned after spring flowering. Some examples are forsythia, mockorange, and lilac. Shrubs that bloom on the current year’s wood should be pruned in early spring before bud break. Among these are St. John’s wort, cinquefoil, and snowberry. This rule does not apply when doing rejuvenation pruning.
Heading back is used to control the size of the shrub or to remove a branch that is out of balance with the rest of the plant. It requires that a branch be removed to a good bud or lateral branch instead of being cut to the ground. Heading back is best done when new growth is complete.
Some old, neglected shrubs can be restored to vigor by pruning all stems or canes to ground level. Among those that respond well to this treatment are: forsythia, weigela, privet, honeysuckle, spirea, and hydrangea. Rejuvenation pruning is best done in late winter or early spring.
Renewal is the removal of old, overgrown stems or canes. This is usually done over a period of three to four years, and 1/3 of the stems are removed each time. It is best done during the dormant season. This results in a more vigorous shrub and, in the case of flowering ornamentals, better flowering.
Shearing is done only when a formal hedge is desired. When shearing, it is important to keep the top of the hedge narrower than the base to allow sunlight to reach the lower branches. The best time to shear is when new growth is complete.