Lilacs can be slow to bloom, and a good show depends upon a pronounced winter chill, soil that’s slightly alkaline, proper pruning and plant maturity. Some hybrid lilacs can take 5 or 6 years before they settle down and begin to bloom. Obviously, you can’t do much about winter weather, but you can prune properly, and add a little lime to the soil around the base of the plant if yours is acidic.
Lilacs develop flower buds for next year’s display where leaves join stems. After bloom, remove spent flower clusers just above points where buds are forming. You can prune to shape by pinching out the tips of nonflowering branches, as well. This will produce two new shoots over the summer months that may develop flowering buds for the following spring.
A little bit of time and some selective pinching and pruning should result in an abundance of fragrant blooms in subsequent years.