Hi, I have a "volunteer" lilac which appeared as a small shrub about 6 years ago. It has continued to thrive, but until 3 years ago, no blooms. My daughter suggested that I apply a lot of lime and lo and behold, the next year we got a couple of blooms! I've continued to lime it in a cool, wet time and over the past 3 years we get a few more blossoms each season. I don't pick them, but leave them alone. Is it the lime or time? Don't know, but you might try it! Good luck.