We have a long Lilac bush hedge. This is the common American Lilac, not the French which I have in another location . The hedge is on the north side, about ten feet off the road, above the road on a slight hill. It has some shade from the south side, but gets about 4 or 5 hours of sun off the road side. It is a mature hedge, I prune it back every other year, it flowers, grew well until this past month. Some of the plants are loosing all their leaves. I can see no bug or obvious insect. The twigs have new buds at their ends, but the green leaves are all gone. I recently mulched it with hardwood chips, as I have done before. Why does it look like it is dieing? =
Please send us photos of the shrubs so we can see what you are dealing with. Send photos of the whole shrub, around the base, and affected foliage.
You may be dealing with site issues, drought, possible disease, etc.
Attached are 1) view of the whole hedge, looking west 2)close up of the north side twigs 3) close up of south (shady) side of "dead" area. At the far (west )end of the hedge, just visible in 1) is the French Lilacs, they are green and seem to be healthy. Thoughts?
We received your photos. The plants may have several issues like a fungal disease such as powdery mildew, a fungal disease; root competition for moisture and nutrients; borers; and improper pruning.
The old fashioned Lilacs can be susceptible to this fungal disease which can be common in the spring during rainy wet weather and warm days followed by cool humid nights. Here is more information on on our website
Pruning - Even though you prune every other year. Heading back the plants are not enough. You will have to do some renovation pruning and thinning not just topping the plant. This opens up the plants to sunlight and good air circulation.
Also, you are dealing with a lot of stems and root competition for moisture and nutrients. Lilacs grow best in full sun in a well drained soil. In 5 hours of sun the plants will grow but flowering may not be as profuse and full.
Take a look a the attached link for renovation pruning. This should be done in early spring. You may not see blooms for several years. https://www.finegardening.com/article/pruning-lilacs
You can prune dead wood now. Scratch the branches with your fingernail and look for green tissue. If you see it, the branch is alive. If brown/gray then it is dead.
Another option is to remove the dead shrubs and plant another species of plant that matches the site conditions. A mixed planting is a good idea so you do not lose the whole stand to an insect or disease issue. Match the plant to the site and plan for mature height and width.
See the information and photo for yearly pruning on the lilacs. This consists of cutting down stems to the ground and yearly thinning. This can be done in late winter/early spring or after bloom in June. Deadheading can be done at this time too. See the photo
Yearly Pruning Keeps Lilacs Under Control by Fine Gardening