Answer: Organic mulches often get moldy. It is a natural part of the decomposition process and you can help avoid it by periodically raking the mulch to incorporate fresh air. Eventually the moisture level will be low enough that mold will stop growing. The mold is harmless to your plants and you don't need to replace the mulch, just rake through it once a month or so to move it around and expose the undersides to fresh air.
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