Answer: Usually, mold or algae on the soil surface indicates the soil is too wet. If this is the case, your plant may also possibly show signs of overwatering. However, in some cases such as a bonsai plant, mossy growth may even be desired and encouraged. Other colors of what looks sort of like a crusty mold may be mineral buildup instead. This would be due to fertilizer use over time or possibly minerals in your water. In either case, simply remove it by gently scraping away a very thin top layer.
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