I have an old dark purple French lilac that only has 2 to 3 blooms a year. I am planning to prune a little after blooms this spring and then fertilize in Feb. of '18. Bone meal will be a component. Does that sound right? This bush was my mother's. Her aunt gave it to her in the '50s.
Old French Lilac
Certified GKH Gardening Expert
Old lilacs will often not bloom or have very few blooms. Yes, adding bone meal and pruning to encourage new wood to grow is a good plan. You can follow one of the two pruning plans described in this article:
The plan should cause flowering to improve over the next 3-5 years.