By Richard Jauron
Extension Horticulturist
Pruning is the selective removal of specific plant parts for the benefit of the whole plant. Pruning shows both the art and science of horticulture. Knowing exactly when to prune is essential when taking care of shrubs to ensure a successful growth.
Horticulturists with Iowa State University Extension and Outreach provide information on when it is the best time to prune shrubs. To have additional questions answered, contact the ISU Hortline at 515-294-3108 or at hortline@iastate.edu.
When should I prune spring-flowering deciduous shrubs?
Spring-flowering shrubs, such as lilac and forsythia, bloom in spring on the growth of the previous season. The plant’s health or condition determines the best time to prune spring-flowering shrubs.
Neglected, overgrown 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, either March or early April. Heavy pruning in late winter or early spring will reduce or eliminate the flower display for two or three years. However, rejuvenation pruning will restore the health of the shrubs.
The best time to prune healthy, well-maintained spring-flowering shrubs is immediately after flowering. Healthy, well-maintained shrubs should require only light to moderate pruning. Pruning immediately after flowering allows gardeners to enjoy the spring flower display and provides adequate time for the shrubs to initiate new flower buds for next season.
When should I prune summer-flowering deciduous shrubs?
Summer-flowering shrubs, such as potentilla, Japanese spirea and panicle hydrangea bloom in summer on the current year’s growth. Prune summer-flowering shrubs in late winter or early spring. The pruned shrubs will bloom in summer on the current season’s growth.
When should I prune “non-flowering” deciduous shrubs?
All shrubs flower. However, the flowers of some deciduous shrubs, such as winged euonymus (burning bush), alpine currant and fragrant sumac are small and inconspicuous. These shrubs possess attractive foliage, fruit, bark or some other ornamental feature. Prune shrubs with inconspicuous flowers in late winter or early spring before growth begins.
When should I prune evergreen shrubs?
Prune narrow-leaved evergreen shrubs, such as juniper and yew, in early April before new growth begins. Light pruning may also be done in mid-summer. Avoid pruning narrow-leaved evergreens in fall. Fall pruned shrubs are more susceptible to winter injury.