Q.Japanese Lilac Tree
We have a Japanese lilac that appears to be thriving, aside from the fact that in its second year bore no blossoms. Is this common? The tree is now in its third spring, is approximately 12 feet high, and is now fully leafed on May 6.
Here are some articles that may help pinpoint the cause.
I would suggest a soil test to determine if too high of nitrogen levels exist in the soil.
To much nitrogen will inhibit flowering.
https://www.gardeningknowhow.com/ornamental/shrubs/lilac/japanese-lilac-information.htm
https://www.gardeningknowhow.com/ornamental/shrubs/lilac/lilac-bush-not-blooming.htm