Root rot

Root rot is a condition found in both indoor and outdoor plants, although more common in indoor plants with poor drainage. As the name states, the roots of the plant rot. Usually, this is a result of overwatering. In houseplants, it is a very common problem, and is slightly less common in outdoor plants. The excess water makes it very difficult for the roots to get air that they need, making them rot.

A large number of root rots are caused by members of the water mould genus Phytophthora. Perhaps the most aggressive is Phytophthora cinnamomi.