The answer to 'retaining wall dying plants' is that there are several common causes, including poor drainage, soil compaction, and insufficient nutrients. Symptoms may include wilting, yellowing leaves, and stunted growth. To address this issue, you may need to improve drainage, aerate the soil, and amend it with compost or fertilizer.
If the problem is severe or you are unsure of the cause, it's best to consult a professional landscaper. They can assess the situation, identify the root cause, and recommend the appropriate solution, which may involve rebuilding or repairing the retaining wall.