have the soil tested first

Is it full sun?

tj

It is in full sun.

Does she prune the shrub? A common mistake. Lilacs are very particular in that the only time to safely prune and still have flowers is within 2 weeks of blooms' wain. Any other time and you are risking removal of flower buds for the next cycle. Of course, pruning at the incorrect time will never kill or harm the health of the plant.

Every time I have been asked this question of a seemingly healthy lilac not blooming, the reason I found was the lilac was trimmed back after mid-summer (July) and the flower buds, which form on the tips of the new growth, were cut off and the plant did not have enough time to form new flower buds. Lilacs like a sweet soil....the addition of a little lime to the soil in the root zone will improve the color, size and abundance of flowers.