Lilacs have a tendency to get quite large and dense with age, so trying to control this plant can become an issue. Lilacs should be pruned in the spring right after they bloom. Begin by removing the dead wood. Then remove some of the oldest stems and finally cut off the smaller suckers at ground level.

If you do those 3 steps every year, you will always have vigorous new growth and the shrub will stay relatively short. In the case of a very large unruly Lilac, cut off the whole plant at ground level and it will regrow nicely. Another way of controlling a very large Lilac is cut 1/3 of the largest stems off at ground level each year and you will have control of the Lilac in 3 years.