Root rot

📖 Overview

Root rot is one of the most common killers of potted plants, seedlings, and vulnerable crops like strawberries and tomatoes in our climate. It happens when roots are starved of oxygen in waterlogged soil, allowing root-rotting fungi and water moulds—chiefly Pythium, Phytophthora, and Rhizoctonia—to colonize and destroy the root system. The plant wilts and yellows from the bottom up, even though the soil feels wet, because the damaged roots simply cannot absorb water or nutrients anymore. This is a high-urgency problem because it can kill a plant in days to weeks once it takes hold, and the window of intervention is narrow.

Root rot typically strikes hardest in spring (March–May) when seedlings are tender and soil temperature is cool, and again in autumn (September–October) if autumn rains coincide with poor drainage. The first sign is yellowing of lower leaves while the soil remains moist—a telltale contradiction that should trigger immediate inspection. Gently ease the plant from its pot and look at the roots: healthy roots are white or pale tan and snap cleanly; rotted roots are brown, mushy, and fall apart in your fingers. You may also notice a sour or unpleasant smell, which is decay releasing gases.

Root rot is easy to confuse with drought stress, but the key difference is the soil moisture: a drought-stressed plant wilts in *dry* soil and recovers when watered, while a root-rotted plant wilts in *wet* soil and does not recover. Another look-alike is nutrient deficiency, which yellows leaves more evenly and does not blacken or soften the roots. Once you spot mushy brown roots, action must be swift—the infection spreads rapidly through the root zone and can be lethal within 1–2 weeks if left unchecked.