An important aspect of pruning is knowing when to prune plants. Proper timing helps to insure attractive, healthy, productive plants. The proper time to prune various woody plants in the yard and garden are indicated below.
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 the lilac and forsythia. The proper time to prune spring-flowering shrubs is largely determined by their condition and the amount of pruning required.
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 (mid-February to early April) before the plants begin to leaf out. While heavy pruning in late winter or early spring will reduce or eliminate the flower display for a few years, the restoration of a healthy, vigorous shrub is more important.
If spring-flowering shrubs need only light pruning, prune them immediately after blooming. Pruning immediately after bloom allows the gardener 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 Japanese spirea, bloom in summer on the current year's growth. Prune these shrubs in late winter or early spring. Summer-flowering shrubs pruned from mid-February to early April 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.
Don't prune deciduous shrubs in late summer. Pruning shrubs in August or early September 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.
Prune evergreen shrubs, such as juniper and yew, in late March or early April before new growth begins. Light pruning may also be done in late June or early July. Avoid pruning evergreen shrubs in the fall. Fall pruned evergreens are more susceptible to winter injury.
The best time to prune deciduous trees is late winter or early spring (February, March, and early April) before they begin to leaf out. Some trees, such as maples, "bleed" heavily when pruned in late winter or early spring. However, the heavy bleeding 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.
If possible, avoid pruning deciduous trees in the spring as they are leafing out. At this time, the tree's energy reserves are low and the bark "slips" or tears easily. Another poor time to prune is during leaf drop in the fall.
An excellent time to prune spruce and fir is late winter when they are still dormant. Spruce and fir possess side or lateral buds. The pruning cut should be just above a side bud or branch. Pines are pruned in early June to early July when the new growth is in the "candle" stage. Pinching or snapping off one-half to two-thirds of the candle reduces the pine's annual growth.
Unwanted lower branches on all evergreen trees can be removed in late winter.
The best time to prune fruit trees is late February to early April. Fruit trees pruned in fall or early winter may be susceptible to winter injury.
Prune grapevines in March or early April. Grapevines pruned at this time of year will bleed heavily. However, the bleeding will not harm the vines.
The upper portions of modern roses, such as hybrid teas, floribundas, and grandifloras, typically winterkill due to exposure to low winter temperatures and extreme temperature changes. Gardeners should prune out the dead wood after the winter protection is removed from modern roses in late March to mid-April.
Old garden roses, hybrid rugosas, and other hardy roses often survive Iowa's winters with little or no winter injury. Those that bloom only once a year should be pruned immediately after flowering. Those that bloom throughout the summer should be pruned in March or early April.
Clematis varieties are often placed into groups based on their flowering characteristics. Some varieties bloom in June and July on the current season's growth. Others bloom on stems from the previous season's growth and again in late summer on new wood. Despite these differences in flowering characteristics, pruning practices for the types commonly grown in Iowa are basically the same. Simply wait until growth begins in early spring and then prune out all the dead wood.
This article originally appeared in the February 11, 2000 issue, pp. 9-10.