Pruning is key to keeping your shrub healthy and able to produce plentiful flowers every year.
When to Prune Lilacs
Prune lilacs in late spring or early summer after flowers fade.
Do this annually to maintain good shape, support healthy growth, and facilitate abundant flowering the following year.
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Fertilizing withbone meal can elevate pH.Fertilizers high in phosphorus support flowering.
Feed lilacs in early spring.
A sharp, sterile hand pruner is the best tool for the job.
Begin by removing older branches at ground level.
Branches 2 inches in diameter can also be removed to make room for new, more vigorous stems.
Head back pencil-thin stems to give shrubs a fuller, more compact appearance and deadhead faded flowers.
A second approach to fixing an overgrown lilac is to cut the entire shrub to ground level.
This can be successful, but is generally not recommended.
Larvae are fairly large and just a few can do considerable damage to affected hosts.
Monitoring activity is important for treatment to be effective.
Lilac Pruning Tips
Overgrown lilacs benefit from aggressive pruning done carefully over two to three seasons.
Rejuvenate the shrub by removing older canes at ground level and selectively heading back smaller branches.
Prune out no more than one-third of the shrub at each session.
Eventually, the shrub will cease to flower completely.
Lilac Borer (Also Known As Ash Borer).University of Massachusetts, Amherst
