Hi Willobie,

There are several reasons that lilacs fail to bloom. You've already gotten some of them. Here's the most common reasons.

Not mature enough as it can take 5 to 7 years for new sprouts to bloom.
Not enough sun as they like full sun - 6 hours or more.
Too much nitrogen from fertilizers, especially if grown in or near a lawn that is fertilized. Causes lush leaf growth at expense of flowers.
Pruned at the wrong time in the wrong way. Remove spent blooms within two weeks of finish of bloom as they set their buds for next years bloom then. Rejuvinate old shrubs by cutting the oldest trunks to the ground. Do one third of shrub a year.
Lilacs prefer a more alkaline soil. If the soil is acid, add a cup of lime every couple of years to the base of the shrub and gently scratch in.

Here's some handy links:
http://spi.8m.com/care.htm
http://lilacs.freeservers.com//lilac_tips.html
http://www.lilacs.com/frames/care.htm
http://gardencenter.southernstates.c...ilactree.shtml


Pruning info:
http://www.gardenersnet.com/lilac/lilac02.htm
http://www.ipm.iastate.edu/ipm/hortn...993/lilac.html

Newt