When rugs stay wet too long, they become mildewed and, eventually, suffer dry rot. The classic example is dry rot caused by a potted plant placed on a rug. The typical result is a horribly rotted circular area in a carpet that is otherwise in good condition. Don’t even think about putting a potted plant on a rug. No matter how clever you are or if you use a glazed pot or saucer, it may not work. Whether you put a vapor barrier between the saucer and the rug, the rug will get wet. Most importantly, it will stay wet. And unbeknownst to you and will become a rotten mess in an area about one foot in diameter.