Standard Korean Lilac Decline


Only one side of my Korean lilac (standard) appears to have survived the winter. Many of the branches on the left are brittle and dry but some are still a bit green when I cut into the bark and look like they have a few dormant buds on them.
Should I give the plant a hard prune when it’s done flowering or just wait it out? I’m facing east taking this photo and while the right side always starts to bud a week or so earlier than the left, the left has not caught up this year.
This isn’t my only plant that looks dead on only one side. My wigelia on the entirely opposite side of my house are also dead looking along one half only.
Any suggestions are appreciated. The lilac has some sentimental value so I’d like to save it.


Thank you for contacting the Toronto Master Gardeners with your question about your Korean Lilac.

It is a little hard to see from the picture the significant difference between the left/north side of your lilac from the right side.

The little detail where you mention the east orientation is a tell-tale clue to your observation. If you are facing east taking the photo, that means the more robust side which happens to also bloom sooner is receiving more sun since it is facing south.  The symptoms are consistent with the left receiving less sun exposure, therefore the shrub puts more energy where it receives the most benefit and lesser so on the north/left side.

While it would be nice if we could rotate the shrub from time to time to create balance,  something more realistic and practical would be to use a balancing pruning.

By carefully thinning out the south/right side, this should let some more light to filter through, thus increasing the vigor of the left side. Also pruning out weaker branches and deadheading immediately after first bloom will return more energy to the host and enhance the second bloom. Similarly deadheading immediately after successive blooming will also enhance following springs blossom.

Let’s also consider the dieback may be the result of something else. Often once a plant is stressed and starts to decline a secondary problem can set in. Like a pest or disease. You mentioned a weigelea in decline as well. Spend some time looking for signs and symptoms on the bark of both these plants. In particular Oystershell Scale.


Lilacs generally do not rely on much fertilizer, but if you want you can do so lightly with a balanced shrub  fertilizer.

Good luck.