The answer to 'why is my mulch brown patches' is that brown patches in mulch are typically caused by a buildup of organic matter, fungal growth, or improper mulch application. This can happen when the mulch decomposes over time, creating areas that appear darker or discolored.
Some common causes of brown mulch patches include insufficient mixing of the mulch, not spreading it evenly, or letting it sit for too long without refreshing. Overwatering, poor drainage, and too much shade can also contribute to this issue. To fix it, you'll need to remove the affected mulch, mix in some fresh material, and ensure proper coverage and airflow.