Answer: You can renovate your lilac bushes but the best time is in the early summer, immediately after they have finished blooming. This is because lilacs spend the summer months developing flower buds for next spring's floral display. If you prune this late in the year, you'll lose next spring's flowers.
To keep your lilacs looking neat and compact, and to encourage lots of flowers, you should trim your shrubs back in early summer on an annual basis. As soon as the last flower is spent, prune your lilacs by removing old wood and pruning off about a third of the height and width. All summer your lilac will produce new stems and leaves and it will also develop flower buds for next spring.
Best wishes with your lilacs!
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