The answer to 'why is my mulch bare spots' is that there are several common causes for bare spots in your mulch. Mulch can thin out or disappear over time due to decomposition, displacement from weather or foot traffic, or uneven application. Bare spots may also be caused by poor soil conditions, plant competition, or pest damage.
To fix bare mulch spots, you'll need to replenish the mulch layer to the recommended 2-4 inch depth. Before adding new mulch, inspect the area for any underlying issues like compacted soil or weed growth that should be addressed first. If the problem persists or you're unsure of the cause, it's best to consult a professional landscaper who can assess your specific situation.