Answer: The mushrooms are growing because the mulch material is decomposing. It's not unusual for this to happen with fresh mulch, especially if it is retaining a lot of water. The best control method is simply to knock the mushrooms down as you rake through the mulch. Raking with incorporate some air which will dry the mulch out a bit and the mushrooms will stop appearing. Rake through it a couple of times this summer while it is still fresh and new. As the mulch material ages it will dry out and not be so conducive to sprouting mushrooms. Best wishes with your flower bed.
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