Plants are not receiving enough sunlight.
Use a lopper or hand saw to remove a third of the thickest stems at the base. Do this every year until all large stems are removed. Rejuvenation pruning is a technique for smaller, densely-branched lilacs like Korean or Meyer lilacs (Syringa meyeri) that have become overgrown.
Apr 02, How to Prune Lilac Bushes. When pruning lilacs, cutting back the tops of overgrown stems is oftentimes not enough. It is generally better to cut the entire stem. Trimming lilacs is best accomplished using clippers. Remove spent blooms all the way to the stems to prevent seeding and encourage more blooms later on. Cut back about a third of the bushleaning.clubted Reading Time: 2 mins.