Root rot is the umbrella term for decay of a plant's roots by soil-borne or water-borne pathogens. On cannabis the main agents are the water mould Pythium, Fusarium species, Rhizoctonia solani and occasionally Phytophthora. Healthy roots are white to cream and firm; rotting roots turn brown, soft and hollow, and the outer layer slides off. Rot at the base of the stem is called crown rot.
In practice
Root rot usually follows a weakness: warm water, little dissolved oxygen, waterlogged pots, compacted media or salt damage. In hydroponics, solution held above roughly 24-26 °C (75-79 °F) with poor aeration is the classic setup. Plants droop in the heat of the day, yellow, stall and do not respond to feed. Growers diagnose by pulling a plant and smelling and pressing the roots: a sour or rotten smell and slime mean pathogens. Fixing the cause, removing badly hit plants, cleaning the system and restoring oxygen come before any product.
Don't confuse with
- Tea-coloured roots: stained by additives or organic inputs but still firm.
- Overwatering: low oxygen alone, reversible before pathogens take hold.
- Root aphids: insects on roots, not decay.
