My lilacs were obtained from pulling some roots from someone else's trees 3 to 4 years ago. They will not bloom. Why?
Certified GKH Gardening Expert
There are various reasons why this can happen, including a lack of phosphorus in the soil. This can be remedied by adding bone meal. Here are some others reasons why your lilac may not be blooming: https://www.gardeningknowhow.com/ornamental/shrubs/lilac/lilac-bush-not-blooming.htm