An important aspect of pruning is knowing when to prune plants. Proper timing helps insure attractive, healthy, productive plants. The proper times to prune various woody plants in the yard and garden are indicated below.
Deciduous Shrubs--Many deciduous shrubs are planted in the home landscape for their attractive flowers.
Spring-flowering shrubs bloom in the spring on the growth of the previous season. Two widely planted examples are lilac and forsythia. The proper time to prune spring-flowering shrubs is determined by their condition.
Old, neglected spring-flowering shrubs often require extensive pruning to rejuvenate or renew the plants. The best time to rejuvenate large, overgrown shrubs is late winter or early spring (March or early April). While heavy pruning in late winter or early spring will reduce or eliminate the flower display for a few years, the long term health of the shrubs is more important.
If spring-flowering shrubs need only light pruning, prune them immediately after bloom. Pruning immediately after bloom allows gardeners to enjoy the spring flower display and gives the shrubs adequate time to initiate new flower buds for next season.
Summer-flowering shrubs, such as potentilla and spirea, bloom in summer on the current year's growth. Prune these shrubs in late winter or early spring. Summer-flowering shrubs pruned in late winter or early spring will still bloom in summer.
Many deciduous shrubs don't produce attractive flowers. These shrubs may possess attractive bark, fruit, or fall leaf color. Prune these shrubs in late winter or early spring before growth begins. Don't prune deciduous shrubs in late summer. Pruning shrubs in July or August may encourage a late flush of growth. This new growth may not harden sufficiently before the arrival of cold weather and be susceptible to winter injury.
Evergreen Shrubs--Prune evergreen shrubs, such as juniper and yew, in late March to mid-April before new growth begins. Light pruning may also be done in late June or early July.
Deciduous Trees--While deciduous trees can be pruned anytime during the year, the best time to prune is late winter or early spring before the trees leaf out. Some trees, such as maples, bleed heavily when pruned in late winter or early spring. The heavy bleeding, however, doesn't harm the trees. The trees won't bleed to death and the flow of sap will gradually slow and stop.
To prevent the spread of oak wilt, avoid pruning oaks from April 1 to July 1. Pruning oaks during this period may attract sap beetles carrying the oak wilt fungus to the pruning cuts and transmit the disease to healthy trees. An excellent time to prune oaks is February and March.
Fruit Trees--The best time to prune fruit trees is from late February to early April. Fruit trees pruned in fall or early winter may be susceptible to winter injury.
Grapes--Prune grapevines in March or early April. Grapevines pruned at this time of year will bleed heavily. The bleeding, however, is not a problem.
Raspberries--All raspberries should be pruned in March or early April. Summer-bearing raspberries also require summer pruning. Remove the old fruiting canes of summer-bearing raspberries after the summer crop has been harvested. Also, pinch out the shoot tips of purple and black raspberries when the new growth reaches a height of 36 inches.
Specific details on pruning can be found in Pm-1304 "Pruning Shade and Flowering Trees," Pm-780 "Pruning and Training Fruit Trees," and Pm-214 "Growing Raspberries at Home."
This article originally appeared in the February 10, 1995 issue, p. 10.