The house we moved to winter of 2012/2013, already had 5 well established lilacs growing.
I have no idea how old they are. They are monstrously large. I'm not good at judging height, but the tops of them are level with our 2nd floor bedroom windows.
I did NOTHING in the garden until after they bloomed last year.
Then we went about pruning them after the blooming was done. I now read that's when you're supposed to do pruning. We just did it then because we didn't want to cut the blooms off! lol
This spring, we did a little pruning on the one around the mailbox... to make sure the mail carrier wouldn't get a face full of bumble bees when leaning in to deliver our mail.
We will again be pruning after they're done blooming. At least to keep them from getting tangle-ish or hanging over the path, or whatnot. I've been trying to look into how much we should prune them... if maybe they should be pruned more aggressively. My husband is very tentative about pruning them. I had to talk him into taking out the branches that were likely to be a nuisance to our mail carrier. ha ha. He would let them grow into a wild blur of lilac bushes like they were when we first moved here.
I now read that you're supposed to clip the blooms off? We didn't do that last year. When they got all dried up, and I noticed they started falling to the ground, I went around with the wheel barrel, picked up the ones on the ground, and just started grabbing the dried ones off the bushes as far up as I could reach. And then made my husband go around & get ones he could reach.
And we did nothing to them the rest of the summer.
All of ours bloomed profusely last spring, and most are in full profuse bloom this year right now.
If lilacs get anymore blooms than this I think the entire neighborhood would smell like someone was taking a bubble bath in an olympic size swimming pool. ha ha
We do have one bush that is NOT in the front yard. That one blooms too, but it doesn't bloom as profusely.
It gets mainly midday and afternoon sun.
The ones in our front yard get morning & midday sun only.
Don't know if that makes a difference.
I think the one that's not in the front yard is in extremely well draining soil that is quite toward the alkaline.
I think ALL of our soil here is leaning toward alkaline, or at best neutral pH.
Here are pictures from the past week:
Oh, and another thing I noticed. The one in the front yard with the darker blooms does have less blooms. And the one that's not in the front yard is the same type.
This is what I'm talking about:

The ones that look like this don't have as many blooms.
I assumed the variety is just a lesser-bloomer???
I have no idea the difference.
My neighbor has one that looks like this though a bit smaller (probably more aggressively pruned judging by the rest of her plants/shrubs/trees), and it's blooming about the same amount.