Troubleshooting
Common Lilac problems — and how to fix them
Common Lilac (Syringa vulgaris) is generally forgiving once you match its basics, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Powdery mildew
A near-universal late-summer cosmetic problem; leaves develop a grey-white coating. It rarely harms the plant. Improve airflow, site in full sun, and clear fallen leaves.
Poor flowering
Caused by too much shade, over-feeding with nitrogen, pruning at the wrong time, or insufficient winter chill. Lilacs bloom on old wood — prune right after flowering, not later.
Excessive suckering
Vigorous root suckers can form a thicket and sap the main plant. Remove unwanted suckers at ground level annually unless propagating.
Lilac bacterial blight and borer
Blackened shoots signal bacterial blight; sawdust at the base signals lilac borer. Cut out affected wood to clean tissue and keep the plant vigorous to limit attack.
Prevent common lilac problems before they start
Most common lilac issues are care-mismatch, not bad luck. Dial in the basics:
Looking for common lilac in general rather than its problems? Read the full common lilac care guide — light, water, soil and feeding.
Common Lilac problems — FAQ
Why is my common lilac powdery mildew?
A near-universal late-summer cosmetic problem; leaves develop a grey-white coating. It rarely harms the plant. Improve airflow, site in full sun, and clear fallen leaves.
Why is my common lilac poor flowering?
Caused by too much shade, over-feeding with nitrogen, pruning at the wrong time, or insufficient winter chill. Lilacs bloom on old wood — prune right after flowering, not later.
Why is my common lilac excessive suckering?
Vigorous root suckers can form a thicket and sap the main plant. Remove unwanted suckers at ground level annually unless propagating.
Why is my common lilac lilac bacterial blight and borer?
Blackened shoots signal bacterial blight; sawdust at the base signals lilac borer. Cut out affected wood to clean tissue and keep the plant vigorous to limit attack.