The answer to 'why is my retaining wall thin grass' is that there are a few common causes for this issue. Thin or sparse grass growth along a retaining wall is often due to poor soil conditions, lack of sunlight, or excessive runoff from the wall. The soil near the wall may be compacted, have poor drainage, or lack the necessary nutrients for healthy grass growth. Additionally, the wall itself can block sunlight and prevent the grass from getting the full sun exposure it needs.
To fix this problem, you'll need to address the underlying cause. This may involve aerating the soil, adding topsoil and compost, adjusting the grading to improve drainage, or even replacing the grass with a more shade-tolerant variety. In some cases, it may be best to consult a professional landscaper to properly diagnose and resolve the issue.