Answer: Usually, young shrubs do not require much pruning at all unless it is to tip back a branch that is growing out of balance. Viburnums in general require very little, but lilacs should be pruned annually in late spring right after they have bloomed. Remove any suckers smaller than a pencil, and once the shrub has matured, remove a portion of the oldest trunks every spring by cutting them off at the ground. This will keep the shrub growing vigorously over time. Do not prune later in the season, howver, because this will remove the flowering wood for the next year; lilacs bloom on old wood.
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