Keep in mind that many shrubs do NOT need any pruning. In fact, many a nice spirea or forsythia has been misshapen by trying to prune it tightly each year instead of allowing it to grow in its lovely, sprawling, natural shape.
When to Prune Shrubs
The late dormant season is best for most pruning. Pruning in late winter, just before spring growth starts, leaves fresh wounds exposed for only a short length of time before new growth begins the wound sealing process. Another advantage of dormant pruning is that it’s easier to make pruning decisions without leaves obscuring plant branch structure.
However, with flowering shrubs, as a rule of thumb, prune within a month AFTER the shrub flowers to allow plenty of time for new flower buds to form.
Shrubs that bloom on new growth may be pruned in spring before growth begins. Plants with marginally hardy stems such as clematis and shrub roses should be pruned back to live wood. Hardier shrubs such as late blooming spireas and smooth (snowball) hydrangeas should be pruned to the first pair of buds above the ground.
Renewal Pruning for Older or Overgrown Shrubs
Every year remove up to one-third of the oldest, thickest stems or trunks, taking them right down to the ground. This will encourage the growth of new stems from the roots. Once there are no longer any thick, overgrown trunks left, switch to standard pruning as needed.
Pruning Hedges
After the initial pruning at planting, hedges need to be pruned often, usually 1 to 3 times a year depending on the plants used. Once the hedge reaches the desired height, prune new growth back whenever it grows another 6 to 8 inches. Prune to within 2 inches of the last pruning. Most hedges do well when pruned twice a year, in spring and again in mid-summer, to keep them dense and attractive. Prune hedges so they’re wider at the base than at the top to allow all parts to receive sunlight and prevent legginess.
Source: University of Minnesota Horticutural Extension
Mike Zins and Deborah Brown, Pruning Trees and Shrubs, Item # 00628, 1997, All rights reserved
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