The answer to 'mulch turning brown' is that mulch can turn brown for a few common reasons, including decomposition, lack of moisture, or exposure to direct sunlight. This is usually a natural process and not a cause for concern, but it may indicate that the mulch needs to be refreshed or supplemented.
One of the primary reasons mulch turns brown is that it is decomposing over time. As organic materials like wood chips or bark break down, they lose their vibrant color and take on a more muted, brown appearance. This is a normal part of the mulch life cycle and can be addressed by adding a fresh layer of new mulch on top of the existing layer.