How to Trim & Maintain Lilac Bushes

Maintain the growing site to ensure that soil is optimal. Test soil to make sure that it is alkaline or slightly acidic for favorable growth. Soil should be well-drained; lilacs do not like to sit in wet soil.

Prune smaller stems and leaves from the lilac bush when foliage gets too thick so sunlight can get through to the entire bush. Flowering diminishes with shade. Make sure branches from nearby bushes and trees are not infringing on the lilac's sun as well.

Remove individual flowers after they wilt and die. When the bush has finished blooming, immediately prune the lilac, keeping between seven to 10 main stems. Cut off branches when they grow to a diameter of 2 inches to maintain balanced growth of old and new stems.

Remove no more than one-third of the branches every season. This will keep the bush renewing itself about every three years, and will ensure that the lilac bush has a variety of stems of various sizes and ages. Newer stems produce more growth and blooms than the older ones.

Cut branches 1/4 inch in front of a bud when possible. This is called "heading back" a branch and encourages the growth of new stems and foliage during regrowth.

Shape the lilac bush into the form you want by removing stems that do not conform and by heading back others to encourage growth in that direction.

Water the lilacs with at least an inch of water every week. Note rainfall and adjust your watering schedule if the bushes get enough rain.

Maintain a 2- to 3-inch-deep layer of pine bark mulch around the lilac's base to prevent weeds and to conserve moisture and soil temperature. Keep the mulch an inch from the main stem.

Feed lilac bushes with a 5-10-10 fertilizer in early fall only if you want to foster vigorous growth. For typical healthy lilacs, no fertilizer is necessary.