Answer: Organic mulch does need to be replaced or added to periodically as it will decompose over time. It's loaded with all kinds of bacteria, fungi and microorganisms that are doing the decomposing process. That white stuff you see is some type of fungi decomposer at work, but it's not harmful. Mulch will decompose more rapidly if it is moist and it has lots of nitrogen matter. As it dries out and the nitrogen matter is used up by the decomposers, the decay process will slow down. Keep mulch a few inches away from the stems/trunks of plants so that moist conditions don't develop against the plant tissue, which makes it more susceptible to disease and insect problems. Adding more mulch as needed next spring shouldn't be a problem.
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