Answer: There doesn't seem to be any reason at all, does there? Lilacs bloom on new growth so you might try pruning yours back now to encourage new growth. Later this summer you should see developing flower buds on the branches. The only other concern is over fertilizing. If your lilacs are getting nitrogen fertilizer they may put out lots of new growth at the expense of flowers. Try feeding with a low nitrogen, high phosphorus fertilizer such as a bloom booster. By the way, the best bloom in lilacs happens after an especially cold winter. This explains why some years lilacs bloom profusely and other years the blooms seem sparse. Good luck with your lilac!
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