Answer: The mushrooms are growing because the mulch is decomposing. This is a natural breakdown of the mulch material. When it is new and thick it holds just enough moisture to begin the decomposition process. The easiest way to control the problem is to periodically rake the mulch to mix it up so the wet parts come to the surface where they can dry out in the sunshine. Every 3-4 weeks should be often enough. Just use a leaf rake to move the mulch around and that should take care of the problem. As the mulch material ages it will less moist and you'll have fewer - to none - new mushrooms growing.
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