The answer to 'why is my drainage system dying plants' is that a failing or improper drainage system can lead to waterlogged soil, which can suffocate and kill plants. Common causes include clogged or damaged drainage pipes, poor grading that causes pooling, and inadequate drainage capacity for the landscape.
Signs of a drainage issue include standing water, wilting or yellowing plants, and fungal growth. To fix the problem, you may need to clear debris from drains, regrade the landscape, or install additional drainage infrastructure like French drains or catch basins. Severe issues may require hiring a professional landscaper to redesign the drainage system.