Answer: The most common reasons for lilacs not to bloom are too little sun, too much nitrogen fertilizer, and pruning at the wrong time of year. These plants need full sun preferably all day long. Sometimes they become shaded over time when nearby trees grow. These plants do not need a lot of fertilizing, so if for example they are in a lawn area that is fertilized then you probably would not need to fertilize the shrubs again. These plants bloom on old wood that grew the year before, so if you prune them in the early spring you will be removing the flower buds. The best time to prune is right after they bloom. It is also possible that you have another cultivar of lilac with a slightly later bloom season -- there are early, mid and late season bloomers among lilacs. I hope this helps.
Q&A Library Searching Tips