Answer: Depending upon species, your lilacs may already have reached their mature height. But, it's easy to reduce the size of lilacs and to make them neat in appearance. Wait until they finish blooming and cut the branches back by about one third. Expect one or two new shoots to develop wherever you make a pruning cut. Lilac's bloom on the ends of branches, and need a year to develop the flowering buds, so prune right after flowering to give your shrubs a chance to produce new wood and buds for flowering next spring.
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