Like any shrub, a lilac may experience die-off of one portion of the shrub due to weather damage or disease. The shrub isn't ruined and simply requires some maintenance pruning to encourage healthy regrowth of damaged sections. Learning how to remove part of a lilac bush requires understanding the blooming pattern of this lovely shrub. The use of sharp pruning tools and proper trimming techniques limits further damage to the plant.
Examine the plant to determine the location and extent of the damage. Look for brittle branches, wilted leaves or broken areas on the lilac shrub. Extreme damage may require removal of branches close to the ground.
Locate the breaking point of the largest branch. Pruning cuts require placing a cut precisely at the connection with an adjoining branch or above two outward facing buds. For a visual picture, imagine a Y-shaped branch with damage on the right side of the main trunk. Make the pruning cut where the right side of the Y joins the center line, flush with the main trunk.
Choose the correct tool for the job. Pruning shears easily cut through small branches less than 1/2 inch in diameter. Pruning loppers cut branches up to 1 1/2 inches in width. Use a pruning saw for any larger branches. Remove the largest damaged branch by making an angled 90-degree cut close to the nearest adjoining branch. Do not tear away portions of bark if the cut isn't clean. Recut the branch for removal and trim off any hanging strips of bark.
Clip smaller branches directly above a pair of buds (green nubs) or a pair of leaves at least 6 inches below the damaged portion of the plant. The object lies in leaving the healthiest possible branches to encourage plant rejuvenation.
Thin out remaining older wood using the same pruning process for removing small branches. Thinning removes old growth to allow new growth inside the plant and should allow some shaping to the damaged lilac shrub. Select areas for cuts with an outward-facing bud to enough growth away from the center of the plant.