When a lilac's spent flowers are pruned it is called deadheading. In some plants, deadheading can force the plant to produce another round of blooms. In others, it will make next year's blooms larger and more numerous. Unfortunately, neither of these will happen with your lilac bush. However, deadheading a lilac bush's blooms during its first few seasons of growth will encourage it to grow more quickly. That's because removing the flowers diverts seed-producing energy into growing energy. After its first few years of growth, deadheading only serves to clean up the lilac's appearance.
Prune your lilac's inflorescence at the point where it is connected to the branch.
Chop the lilac flowers into small pieces, using a small kitchen knife.
Spread the chopped lilac flowers at the base of the tree as a nutritious recycled mulch. Spread the lilac flower mulch over or underneath it if the plant already has organic mulch.