Lilacs come in different sizes, colors and bloom times, but if you care for your lilac it will, without fail, produce large, fragrant, colorful blooms every year. To get a lilac bush to bloom more than the few small blooms you might be seeing now, you'll need to give it a little extra care. The timing for when you work with your lilac depends solely on the bloom time of your lilac variety. While lilacs require very little to bloom successfully, with careful attention annually, you should see large, full blooms.
Fertilize the lilac with a general purpose feed according to the package instructions when you first see the buds beginning to enlarge and swell, usually in early spring. Wait for the flowers to bloom and begin to dry before moving ahead to step 2.
Deadhead each stem of the lilac by cutting off the dried blooms just behind where they begin. Use sharp hand pruners and make a diagonal cut which leaves the cut side of the stem facing downward.
Cut out dead wood by looking over the lilac to spot diseased or damaged stems and find their base along the ground. Cut the stem clean across at ground level and pull the dead wood away from the rest of the plant.
Fertilize the plant again after the dry blooms are clipped with the same fertilizer method and dosage as you used in step 1.
Spread a 3-inch deep layer of mulch around the perimeter of the lilac to block weeds and retain water in the soil. The circle of mulch can be up to 3 feet in diameter.
Repeat this process each year to ensure many flowers, with the exception of step 3, which should only be carried out every three to five years or your plant may actually decrease blooms as it tries to recover from excessive pruning.