Now is the time to trim lilacs bushes. Lilacs will set the flower buds for next years flowers during this season. Now that lilacs are done flowering for this year, it is time to do any trimming and shaping that you want to do so that you preserve next year's flowers. For austetic reasons you can also trim off the spent flowers & seeds from this year's flowers.
|lilac's spent flowers & seeds|
We inherited a lilac bush when we bought our house. It is planted right against the house. Although I love the flowers and smell of lilac in the spring, it is a big bush and I would have preferred a smaller one so close to the house. I try to keep it pretty short, but last year I didn't get it cut back & so it was quite tall this spring. This weekend I spent some time trying to trim it back to a size I'm happier with, but in the process it took a pretty drastic cut back.
Typically it is recommended that you do not remove more than 1/3 of a plant when trimming. This year I cut the lilac back by about 1/2, but I am not worried about it because I know that lilacs are a very resilient bush that can be almost impossible to kill. It is a little ragged looking, but I didn't want to take off any more leaf area this year. In a couple of weeks, after it has filled in a little again, it will look better.
Happy Gardening! :)