How to coax poorly blooming lilac bushes to bloom more profusely?

Most people are afraid to prune and limb up large bushes. Even smaller plants. But, pruning will definitely help. Gets rid of old wood and allows the plant to use its nutrients more efficiently by not trying to grow more but to grow better. That way you'll get better blooms, not necessarily more.

prune them after they are done blooming.

www.gardenguides.com/96627-lilac-bush-bloom.html

Thin it

Prune after blooming!

Hi there, pruning or trimming your lilac bushes will encourage new growth and lots of blooms. Here's a great article and video that will show you how and when to prune your lilac bush https://www.thespruce.com/pruning-lilacs-how-and-when-to-prune-lilacs-1403004