Root Rot
Definition: Root rot is the decay of a cannabis plant's root system, usually caused by waterborne pathogens like Pythium thriving in warm, oxygen-poor conditions. Healthy white roots turn brown, slimy, and foul-smelling, so the plant wilts and yellows even when wet, because damaged roots can no longer absorb water or nutrients.
How Root Rot works
Roots breathe. When they sit in warm, stagnant water or soggy soil, oxygen runs out, root tissue weakens, and opportunistic organisms move in. Pythium is the best known, and it’s the same family of pathogens behind damping-off in seedlings.
Symptoms above ground
- Drooping that doesn’t improve after watering, or gets worse.
- Yellowing and browning leaves that look like nutrient problems.
- Slow or stalled growth.
Symptoms below
In hydro you can see it directly: roots go from bright white to tan or brown, feel slimy, and smell like a swamp. In soil, gently slide the root ball out of the pot; mushy brown roots and a sour smell confirm the problem.
Where it starts
- DWC and other reservoirs above about 72°F (22°C).
- Failed air pumps or too few air stones.
- Containers without drainage holes, or soil kept constantly wet through overwatering.
- Dirty equipment carried over from a previous grow.
Recovery
In hydro, change the solution, clean the reservoir, cool the water to 65 to 68°F (18 to 20°C), increase aeration, and trim away dead roots. Many growers add beneficial microbes such as Bacillus or Trichoderma products to help healthy roots outcompete pathogens. In soil, let the pot dry down and improve drainage. Plants with some healthy roots left often push new white growth within a week; plants with almost none rarely recover.