As wood chips sit in a large pile, they will naturally heat up and start to decompose. As this happens, mushroom mycelium will start to grow on the wood chips and break them down. This may look like a white or green mold growing on the wood chips. There may also be a powdery substance that floats in the air when you disturb the pile. This is all normal wood chip behavior, and is actually very beneficial to your soil and garden.
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