Answer: The timing depends upon the type of shrubs you're growing. If your hedge is one that does not flower, you can trim in the spring, just as new growth begins, so the new growth will cover any bare stems that result from trimming. Depending upon the size of the shrubs (and how many you have), you can prune by hand or with an electric hedge trimmer. A formal hedge looks best when squared off - something that's easiest to accomplish with a hedge trimmer. An informal hedge can be pruned by hand, varying the lengths of the stems to make it more natural in appearance.
Flowering shrubs are best trimmed immediately after flowering (you don't want to prune off any of the flowers!)
Hope this answers all your questions!
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