Pruning lilacs every year is essential if you want a perfectly-shaped tree. Some grow to about 8 feet in height but others can be as tall as 30 feet. Lilacs should be trimmed after they are done blooming. This will give new shoots time to develop. Lilacs bushes should not be so dense that sunlight and air cannot reach the center. Pruning lilacs improves their form and appearance and encourages good health and many blooms.
Cut off most shoots and small suckers that grow at the base of the lilac bush. These cause a messy appearance and leech nutrients from the rest of the plant. You may want to leave a few of the healthier, stronger shoots in place.
Identify large stems in the center of the lilac that may be blocking sunlight and air ventilation. Removing large stems inside the canopy helps avoid visible stubs. Cut them with hand pruners at the joint they share with other branches. This will give newer shoots more room to grow.
Clip off branches that stick out from the lilac bush and mar its appearance. Make the cuts next to buds.
Prune mature lilac bushes that have gotten out of control by focusing on removing one-third of the bush every year. Cut the oldest stalks down to the soil. This will encourage new ones to grow in their place, revitalizing the shrub.
Cut bushes down to the ground if they are unhealthy or unsightly. In the early spring, cut down each shoot to just above ground level. New stalks will grow during the following season.