Shrubs need to be trimmed or pruned at different times during the year. The main purpose of pruning is to promote growth of foliage and blossoms. Pruning is also done to shape a shrub and control its height. It improves plant health by improving circulation of air and sunlight. Early flowering shrubs are pruned at later times than late-flowering shrubs. Rose shrubs have varying pruning times.
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Spring-flowering shrubs bloom on wood that grew the previous season and need to be pruned after they have flowered. If pruned before, the flower buds are likely to be removed, resulting in little or no blooms that season. Spring-flowering shrubs include the lilac, honeysuckle, weigela, bridal-wreath, forsythia, quince and pea-shrub.
Flowers on shrubs that bloom in summer grow on wood that has grown during the current season. These shrubs need to be pruned in early spring, months before flowering. Pruning early will avoid removing wood with buds forming for the current season. Among the summer-flowering shrubs are the blue mist spirea, butterfly bush, pee gee hydrangea, St. Johnswort and the Rose of Sharon.
Rose bushes require pruning to control shape, promote flowering and remove damaged stems. Most are best pruned in spring when forsythia begins to bloom. Species, or wild, roses require the least pruning; hybrid teas, which bloom all season, the most. Hybrid teas, grandifloras and floribundas flower on current wood and need to be pruned -- hard, to nearly half their height -- in early spring. Shrub roses should not be pruned the first 2 to 3 years.
Types of Pruning
In general, pruning for thinning and shape is performed annually. Rejuvenation pruning -- or trimming the plant to the ground -- is only for failing, poor-flowering shrubs. The following year the shrub should have its health restored, with rich blooms and foliage. However, spring-flowering shrubs will not flower the year they were rejuvenated. Avoid shearing, or cutting straight across the tops of shrubs, unless the shrub is a hedge. The bush may become straggly and skinny.