Syringa vulgaris, commonly known as lilac, is a large shrub that can reach 20 feet in height. As the shrub ages and grows more dense the bottom leaves generally die back, giving the lilac an unattractive shape. Pruning the Syringa vulgaris is not only required for aesthetic purposes, it is also important for the health of the plant and contributes to more and bigger blooms. Prune the Syringa vulgaris immediately after it has finished blooming.
Remove all damaged and dead stems. Cut them back to their points of origin.
Remove any growth thinner than a pencil.
Cut off all but one sucker (small sprouts from the soil at the base of the plant). Cut the remaining suckers to 1 inch below the soil.
Remove all but six to 12 of the main stems from the plant. The remaining stems should be separated so that they don't rub up against one another. This allows the Syringa vulgaris to receive air and light in the interior of the shrub and also to grow new wood that will produce more flowers.
Control the height of the Syringea vulgaris by removing growth 1 foot below the desired height. Create a rounded silhouette when you remove top growth.