Waterlogging / overwatering root rot
How to recognise it
Yellowing leaves, soft or mushy roots, and a plant that wilts despite consistently wet soil — a common point of confusion with drought stress, which looks superficially similar.
Life cycle and conditions
Occurs when soil or compost stays saturated for extended periods, starving roots of oxygen and encouraging root-rotting organisms; particularly common in heavy clay soil or pots without adequate drainage.
Prevention
Improve soil drainage before planting; raise pots on feet to ensure free drainage; choose pots and compost appropriate to each plant's water needs.
How to treat it
Let compost or soil dry out more between waterings where a plant is otherwise healthy; for advanced root rot, repot into fresh, free-draining compost, trimming away mushy roots.
Not applicable — this is a drainage and watering issue with no chemical fix; improving conditions is the only effective response.