The main reason of hedge trimming is to keep the plant good looking and healthy. Trimming will minimise problems with fungus and diseases. The best time to trim your hedges depends on when the plant blooms. If your shrubs of hedges just have flowers blossom in early spring - trim them after the bloom during summer. If they blossom in late spring is best to trim them in fall or winter. For non blooming hedges - avoid pruning from the time the bud swell to the time the leaves are fully formed. Light pruning can be done in the summer for all types of shrubs and hedges, just to keep them nice.