Prune lilacs right after they finish blooming
Use clean, sharp pruning shears or loppers
Remove dead, damaged, or diseased branches first
Cut spent flower clusters back to a pair of healthy leaves or buds
Thin out up to one-third of the oldest stems at ground level
Remove weak, crossing, or crowded branches
Keep the center of the bush open for airflow and light
Cut back tall stems to shape the plant as needed
Avoid heavy pruning in late summer, fall, or winter
Do not remove more than one-third of the shrub in a single year
Remove suckers growing from the base if unwanted
Clean up all cut branches after pruning
Disinfect tools after use if disease is present