The most likely issue to be experienced with a poorly drained houseplant is root rot. As explained by the University of Wisconsin-Madison’s Division of Horticulture, this is the common name for any number of diseases that kill off a plant by destroying its roots. Many of these diseases are caused by four different species of fungi, which are commonly found in wet soil: Pythium, Phytophthora, Rhizoctonia solani, and Fusarium.
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