Originally Posted by Newt*
I can't help you with the weed and chemical stuff as I don't use it, but if your lilac is in the lawn and not a garden bed, try and have a mulch ring around the base at least 12" out from the outer edge of the shrub base. Lilacs won't flower well if you fertilize your lawn, especially if you use synthetics. If you have tested the pH of your soil and it's a bit on the acid side, scratch a cup of lime into the soil around your lilac. They prefer a more alkaline soil and will flower better for you that way.
Can a lilac tell the difference between a synthetic fertilizer vs an organic based fertilizer?