Some Lilacs Bloom, Some Won’t

Question

I have six lilac bushes in a row. Every other bush is light lavender and the opposite bushes are a dark purple. The light lavender bushes are in full bloom, but there’s not a bud to be found on the dark purple bushes. Can you explain?

Answer 1

Most likely they have slightly different nutrient needs. I would recommend giving the area a little more phosphorus. It won't hurt the light colored ones and will help encourage the darker ones to bloom.