it usually grows due to high humidity AND a lack of ventilation, which is the main thing. you can have high humdiity and not get mold, its the ventilation thats the key. it happens in taller enclosures, glass ones with solid lids (ie not screen or mesh). also if the soil is too wet, standing water can go bad and cause mold problems on uneaten food and the like. but ventilation is the key. replacing the living plants with fake ones doesnt really solve the problem much. it would be interesting to know what kind of enclosure you use (dimensions, lid, material, size etc). in short, increased ventilation reduces mold, decreasing humidty helps too.