What is the primary cause of root rot in container-grown plants?

Overwatering is the primary cause of root rot in container-grown plants because excessive moisture creates conditions that are highly conducive to fungal and bacterial growth. When soil remains saturated for extended periods, the oxygen levels around the roots diminish, leading to anaerobic conditions that favor pathogens responsible for root rot. Healthy roots need oxygen to function properly; when they are deprived of it due to overwatering, they become weak and susceptible to rot.

In addition to overwatering, inadequate drainage can contribute to root rot; however, the direct action of excessive water is often the more immediate trigger for rot symptoms to manifest. Soil compaction can impede proper water movement but is not the root cause itself. Similarly, insufficient light affects plant growth and health but does not directly lead to root rot. Thus, while poor drainage and environmental factors play roles in the health of container plants, overwatering stands out as the main culprit leading to root rot.