It looks like it is growing in a cave!! That doesn't look a good location for a lilac, without adequate sunlight and in such a restricted area. Lilacs perform best in full sun...6 or more hours a day. Any less and they will be sparse and not as robust and not bloom heavily or much at all. And they appreciate being out in the open so they can grow without obstruction and with good air circulation and that will greatly diminish the potential for any diseases.

Otherwise they need minimal care - rarely ever need fertilization (many sites instruct you not to fertilize lilacs) and not even much pruning, unless you are attempting to renovate an overgrown shrub.

what gal said.. a full blinding sun plant .. suffering in deep shade .. and too close to the house ...

bugs not an issue ...

never needs fert ...

too big to move.. imo ... if you have space in much more sun.. just buy some new ones ... and be done with these ..

or if you can find some new offsets near the bottom.. you could take those ... if you can get any of those with even a single root.. you can pot them and grow some roots and plant them in the ground in fall ...

one other thing.. many have noted very little flowering this year .. for whatever reason ... sometimes the mild winters are worse on flowering shrubs.. than cold ones.. though right next to the house... you wouldnt think weather would be much of an issue ...

ken

Lilacs are prone to honey fungus (Armillaria), it might be worthwhile to look that up and find out how to check for its presence.

It does get substantial amount of sun-here it is today. it is in between two laurels that also recently declined. What i don’t understand is why It thrived for years and now this. I will check into the honey fungus and into planting new smaller ones at the bottom. Thanks for your responses!

That is still not nearly enough sun for a lilac. And while excess shade will not kill them, it can certainly contribute to a decline in vigor and flowering over time.