Sometimes it takes them awhile. The other reasons might be soil is too acidic, ground is too wet, or there is too much shade. If you prunned them, you probably cut off the budding wood. I have also heard of people "shocking lilacs" by cutting into some of the roots with a spade.

Better luck next year!

easiest is to prune right after the (in your case it'll be you checking on your neighbors bushes) the lilacs have bloomed. lilacs only bloom on year-old growth. normally what one does is to cut back the sprout on which the lilac had bloomed. a calous will form, and the plant will put out two new sprouts at that point. on the next year flowers will form on one of these two sprouts, and leaves upon the other. after they bloom, you'll come along with your clippers, and trim away the flowering stem, and the leaf stem. the process will keep on repeating itself, and everybody will be happy.

-d.

I was told by a couple of fellow gardeners to put banana
peelings around by lilac trees. Works wonders!!! for some reason. I put the occasional peelings just under the earth around the bushes. I have lilac with many flowers on fairly young bushes. It certainly doesn't hurt them. Good luck!

If your lilac is in shade it may not bloom at all.

simple answer....do not prune, flower buds are being chopped off

Lilacs should be pruned of crossed over branches and old growth in danger of becoming diseased. Your lilac will not bloom on the pruned section the next year. Lilacs also need to be limed if your soil is acidic. Lilacs need the same conditions as a well manicured lawn and that is why you see so many growing in the middle of a lawn. Some lilacs bloom twice once in the spring and smaller blooms in the fall. Lilacs should also have the dead blossom carefully removed and I am sure you can find information on how to do this on the web. It must be done properly. This causes the lilac to have twice as many blooms set the next year. I have five in my yard and all bloom every year.

My mother always puts wood ash (like from a woodstove, campfire, etc.) on hers, and so do I. I never prune them and they always bloom. They're in mostly sun.

I like the wood ash idea. Iam glad for the info.I will be trying that in the spring.

I once heard here somewhere on the GardenWeb (I'm not kidding), that you must ask it to bloom, not plead for it to necessarily do so, but persuade it gently by asking, "Lilac, are you going to bloom for me in the spring next year...It would make me so happy if you did and I will take good care of you after?" apparently it works. On the other hand, I also think I heard that if you threaten it, it might also work! "If you don't bloom for me this year, you're going out! ....and I mean it!" 8^)

I hadn't heard about most of these remedies.
I had the same problem. Do you fertilize your lawn?
If so, stop the lawn fertilizer from hitting the lilacs, nitrogen grows leaves, not flowers, unless they are pansies. Hit them with bone meal in the spring and fall.

Lots of sun and don' prune in fall or early spring - only immediately after blooming.

Giving lilacs wood ashes have worked great for me in a former garden. I am going to try it on my lilacs that have not bloomed. I have use epsom salts on Rose of Sharon shrubs and it worked wonders. After reading your suggestions I will also try that on my lilacs. Thanks for the tips!
Francie

My lilac tree didnt bloom this year and someone told me that it needed lime and rose fertilizer. Has anyone heard of this or tried it?

This is the third year for my lilac and it is not blooming either. I am wondering if it is lawn fertilizer as daddylonglegs suggested, because the bush looks very healthy. How do I protect it from fertilizer? Cover the bush? Stay a certain distance away?