The answer to 'mulch yellowing' is that it is a common issue caused by a variety of factors. Mulch can turn yellow due to a lack of nitrogen, excessive moisture, or the breakdown of organic materials. Symptoms include a faded, straw-like appearance of the mulch. To address this, you can try adding a nitrogen-rich fertilizer, improving drainage, or replenishing the mulch layer.
If the yellowing persists or covers a large area, it's best to call a professional landscaper. They can diagnose the underlying cause and recommend the appropriate solution, which may involve replacing the mulch entirely or addressing any underlying soil or drainage problems.