I've read your article on non blooming lilacs and have tried your suggestions. I've had these small 4 ft tall lilacs for 20 yrs and never a bloom! I've tried transplanting suckers and even whole bushes to a sunnier location but the most they get is 4-5 hours of sun, and do not flower. They seem to bloom on every side road, untended and wild. Why can't mine bloom?
Lilacs Not Flowering
Certified GKH Gardening Expert
Full sun is 6 plus hours of sunlight, a Lilac needs this amount of sunlight and also the correct amount of chill in the winter to flower.
I would suggest a soil test to determine what may be going on in the soil conditions.
Your County Extension Office can help you with a soil test.
Here is a link to help you locate your nearest office.