The answer to 'why is my mulch dying plants' is that excessive or improper mulch application can suffocate and kill plants. Mulch that is piled too deep or too close to the plant stems can prevent oxygen and water from reaching the roots, leading to plant decline and death.
Common symptoms of mulch-related plant death include wilting, yellowing leaves, and stunted growth. To prevent this, apply 2-4 inches of mulch around plants, keeping it several inches away from the stems. Regularly check that mulch is not too thick or compacted, and replenish as needed to maintain the ideal depth.