Lilac

Question: My well established appears to be dying. Can anyone tell me if it is and what I might do to save it?

responder: An Ask Extension Expert Replied May 17, 2023, 2:03 PM EDT
response: Hello Joanne:    It would be quite helpful if you could fill out this form and attach it to this query. Having more info. about the history of the tree and how it has been cared for, etc. will help us provide accurate/more precise diagnosis.  Thank you.

responder: Betsy, UVM Extension Master Gardener Volunteerwww.uvm.edu/extension/mastergardenerWe do not intend to endorse any products we mention or criticize products we do not mention.When we include a link to a resource that recommends a chemical, it is for informational purposesonly; the chemicals may not be registered for use in Vermont. Replied May 17, 2023, 2:38 PM EDT
response: Hi Joanne, Thanks for your question. I know you were already asked for more information, but I have some specific questions as well. From your photo, it looks like part of the tree has no leaves and no flowers and part is doing well. Is that correct? Did the part without leaves have some leaves that turned brown and developed spots or did they ever get leaves?  You may be able to revitalize it by pruning right after the flowers die back. Lilacs do best if the old flowers are cut off right after blooming, and general pruning can be done then as well. Lilacs can be very responsive to pruning. They should be pruned immediately after they're done flowering in the spring. Since they set next year's flower buds right after the current year's flowers have faded, pruning later in the summer or fall will result in cutting off many or all of next year's flowers.  I am including a reference that will give you an idea of the possible problems and when we get more info from you, we can be more targeted in our response. Though this is from MN, it has a good deal of information relevant to lilacs in other cold weather areas. Also included is a pruning reference for lilacs https://extension.umn.edu/yard-and-garden-news/lilac-issues-season https://extension.umn.edu/trees-and-shrubs/lilacs#pruning-1923160

responder: The Question Asker Replied May 18, 2023, 10:33 AM EDT
response: Here is the form.  Other infomration.  The lilacs have been there for about 12 to 15 years.  Last year I had to cut off 1/2 of it as it was dead. I do prune it right after the flowers are done.  The bushes are planted on a bank of pachysandra  that is mostly clay.    This year it looks worse than last year with brown leaves .  Again it is about half of two bushes.   I am tempted to cut it all down.  I think the weather is about average.  I do not use any chemicals of fertizilers. JoanneOn Wed, May 17, 2023 at 2:04 PM Extension Foundation <<personal data hidden>> wrote:

responder: Betsy, UVM Extension Master Gardener Volunteerwww.uvm.edu/extension/mastergardenerWe do not intend to endorse any products we mention or criticize products we do not mention.When we include a link to a resource that recommends a chemical, it is for informational purposesonly; the chemicals may not be registered for use in Vermont. Replied May 18, 2023, 3:03 PM EDT
response: Thanks for the information Joanne. It sounds like you had success with your lilacs in that area for a long time and you were pruning them appropriately.  You said they are in clay soil. Lilacs like well-drained soil and if the soil has become more compacted over time, that may be the current problem. You could try working in a lot compost and examine what you can as you uncover the roots. The roots may be rotting on the dead side of the plant if it is too wet there. Lilacs grow best in slightly alkaline (6.5 to 7.0 pH), moist, well-drained soil high in organic matter. Have you done a soil test in that area? If the pH is below 5.5, you'll need to add lime to increase the pH. If you just do one thing, I would recommend trying to heavily amend with compost and check some of the roots on the dead side. You certainly could also try rejuvenating it, as you suggested, by cutting it down to about 12 inches from the ground in late winter when it is dormant, but it still will not do well if the soil is too heavy or the pH is not right.  I hope this helps and I wish your lilacs full recovery.