Q: I have had a ‘Sensation’ lilac for several years. It has always produced lovely pinkish purple flowers edged in white. But this year it produced a few odd clusters that had only pale pink flowers.

As I’m sitting at home writing this column, a terrier snores on the ottoman next to me and the heady fragrance of lilacs fills the air. When the “Sensation” lilac burst into bloom this week, I ...