This makes me think my lilacs are coming to the end of their lives. I should probly dig up the best looking suckers and move them into a nursery bed to get some size on them before replanting. My lilacs are ancient. They have been here on my property for 35 years BUT I got them from the house across the road, where they were HUGE old bushes lined up along the road. When the township widened the road, they cut them down and dug them out with a backhoe. We were just moved in here so I asked the guys could I have the big root balls and they brought them over and plopped them down where I had hastily dug planting holes, all along our south border (which was just an open field at that time). Those lilacs had to be at least 40+ years old at that point so the root balls might be 70+ now.
