Answer: Lilacs grow best in rich, well draining soils in full sunshine. Some will perform well in only 4 hours of sunshine. So, if you're sure the soil is well amended and well draining, prune everything down by one third to encourage healthy new growth. If you see no improvement, you may want to dig and move your plant this fall, or at least dig it and amend the soil with compost and then replant it. It sounds like it is struggling and I think both the pruning and amending the soil will help it along. Good luck with your lilac.
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