I’m hoping for some help diagnosing an issue with one of my lilacs.

I have two common lilacs planted side‑by‑side. One is the original shrub that’s been in place for years next to a stone wall. The second was transplanted last September. I expected the transplant to be the slow one this season, but instead it’s the older established lilac that’s showing stress.

Symptoms on the older lilac:

• Sparse foliage compared to previous years

• Smaller leaves overall

• Branch tips look weak and less vigorous

• Color is duller than normal

• Growth noticeably behind the transplanted lilac

Site & care details:

• Full sun most of the day

• Well‑drained soil

• No recent fertilizer changes

• Watering is moderate — not heavy

• No visible pests

• No mechanical damage or pruning this season

What I’m trying to understand:

Why would the long‑established lilac decline while the recently transplanted one is doing well? Could this be root‑zone disturbance, moisture imbalance, late‑summer stress, or something else entirely?

pic 1 was taken on 08/26. pic 2 was taken on 09/18