Answer: Lilacs can take a few years to become mature and established enough to bloom, but in this case I would suspect one of two problems. One is that the location is just too shady; lilacs prefer full sun but will bloom adequately in about six hours of sun if the hours include noon. In a shadier location it is possible it would not bloom much at all. However, since the plant has never bloomed, I am more likely to suspect that it is being pruned incorrectly. Lilacs should only be trimmed in the spring right after they bloom. They bloom on wood produced the year before, so pruning later in the season removes the following year's flowering wood. Finally, if the plant has not grown much, it is possible that it never rooted correctly and is thus stunted. The only way to tell for sure if this is what has happened is to dig it up and possibly transplant it to a better location. You might find, for example, that the roots are encircling themselves and strangling the plant. If this is the case you could try root pruning, trimming back the top to compensate for the root loss, and replanting.
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