I have moved in with my mother, recently. She lives on 11+ acres of ancient farmland that has been allowed to revert to trees wild flowers, over the past 60 years. There are two patches of ancient lilacs that have provided decades of enjoyment. In recent years, despite repeated severe pruning, the shrubs are producing scant blossoms and poor-appearing leaves. No discoloration or evidence of fungal infestation. Can anyone offer ideas? They are 8-10 ft tall, or more, so no problem with baic growth.