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Sandy's Garden

When to Prune Shrubs

Prune at the right time!

By: Sandy Feather ©2007
Penn State Cooperative Extension


Q. There are several shrubs that I still need to prune, and was wondering when is the best time of year to prune them – spring or fall? My list includes burning bush, azaleas, wiegela, an oakleaf hydrangea, red twig dogwood and a bridal wreath spirea.

 

A. Flowering shrubs - The best time to prune flowering shrubs depends on when they produce flower buds. Some plants, including azaleas, bridal wreath spirea, and oakleaf hydrangeas produce their flower buds during the previous growing season. They “bloom on old wood.” Other plants, such as weigela and many hollies, produce their flower buds on the current season’s growth. They “bloom on new wood.”

  
Shrubs that bloom on old wood begin to produce next year’s flower buds soon after they finish blooming. They should be pruned as soon as they are finished flowering so that you do not remove too many of next year’s flowers. Those that bloom on new wood should be pruned in winter or early spring before new growth starts.
  

Burning Bush
Bright fall foliage of a Burning Bush

Burning bush is really grown for its colorful fall foliage rather than its inconspicuous flowers, so you can prune it whenever it is most convenient for you. Red twig dogwoods bloom, but they are grown more for their colorful winter stems than their flowers. Since they produce the best red stem color on young stems, they are usually pruned in the spring. You can cut all of the stems down to within a few inches of the ground. This will force new stems to sucker up from the roots. Not only does this treatment produce the most colorful stems, it is also a great way to keep these vigorous plants in bounds.

If any of these plants are very large and overgrown, consider sacrificing the flowers and pruning them when they are dormant. Early to mid-March is ideal for the plants and the person doing the pruning since we can have very nice weather at that time of year. Severe pruning is not as stressful for plants when they are dormant. If the shrubs are healthy and vigorous, it is fine to prune them back into shape in one session. However, very old plants or those that are not healthy and vigorous should have severe pruning spread over a three year period to reduce the impact of removing so much wood.

Azalea
Azaleas bloom on 'old wood'

It is best to have all pruning finished by mid-July. Pruning forces new growth on actively growing plants, and if that happens too late in the season, the new growth can be killed by cold winter weather. Dead branches or stems should be removed whenever you notice them, regardless of the season.

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