The 0-45-0 won't help.

Most often, the lack of bloom with lilacs is due to insufficient sunlight.

I have a rose garden in the same area and shade is not it's problem. Someone else suggested that it might be planted to deep. I planted it like I've always done in the past. It's a nice bush, I would love to keep it.

When do you prune it?

And how much do you cut off?

It is possible you are feeding it too well. I had the same problem with a lilac at the back of my rose bed. I moved it to an area with much poorer soil and it blooms like crazy every year now.

This is not an uncommon problem :-) In fact, it is a frequent enough situation that if you search under the topic of "lilacs not blooming" you'll come up with numerous hits.

Generally, it's attributed to one or more of the following conditions, so go through a process of elimination to see what it might be.
1) insufficient sunlight - lilacs prefer full sun (6 hours)
2) improper pruning - lilacs bloom on last season's growth so prune immediately after bloom, no later
3) incorrect soil conditions - lilacs prefer a nearly neutral soil, so too acidic a soil condition can impede blooming
4) over fertilizing - too much nitrogen-based fertilizer or too rich a soil will encourage foliar growth over flowers. Make sure any lawn fertilizer applied in the area is well away from the lilac.
5) plant too young - probably not the reason in your case as the plant WAS in bloom when purchased. But most lilac cultivars need to achieve an appropriate maturity before they bloom.
6) it's too dry - while lilacs don't like wet feet, they do react to summer drought stress by not setting flower buds. Make sure it gets sufficient summer irrigation.
7) not the right kind of lilac - again, I doubt that is your problem as this situation is usually reserved for warmer climates where common lilacs do not receive an adequate winter cold period.

I doubt too deep planting is a cause. Typically planting a shrub or tree too deeply simply results in that plant failing altogether, not just failing to bloom. Some gardeners have reported success in sparse flowering lilacs by dosing with a solution of epsom salts - I have no idea whether this works or not. My problems with lilacs is not lack of bloom but rather their sending up suckering shoots throughout the planting area. What a nuisance!

I went back to Watson's Nursery and the person I talked to was stumped as well. She told me to sprinke about a cup of lime around it. She also told me not to dig it up this year because my results won't be know until next spring. So I'm trying to have faith that my beautiful lilac bush will also be beautiful with blossoms next year. Thanks for the help.

I noticed that the leaf buds are swelling and almost ready to open so I picked one off. I peeled away the layers and to my surprise there were blossom buds there. I've waited 4 years for this. Excited is an understatement. So now I have another question.

During the 4 years since it was planted, it has grown to about 6ft. I don't want all the blossoms to be at the top so should I cut it back a couple of feet after it blooms? I know the blossoms are set in late summer so I should be safe and not affect the blooming next year. Am I correct in this? I sure don't want to wait another 4 years for blooms.

What kind of lilac is it? Most of the common lilac culitvars (Syringa vulgaris and hybrids) get to be quite large shrubs.......15-20 feet is not unusual. Since it is a suckering shrub, if you wanted more flowers lower down, I'd suggest cutting back some of the exterior stems to a variety of graduated heights, allowing the interior to grow freely. This should create a more rounded, evenly flowering specimen rather than concentrating the flowering at the top.

Any significant pruning should be done immediately after the bloom period to avoid losing next season's flowers.