From my perspective, the problem begins not with a pathogen, but with water. My roots, like all plant roots, require oxygen to respire and function. When I am planted in a pot without adequate drainage or am watered too frequently, the soil becomes waterlogged. This saturation pushes out the air pockets, creating an anaerobic environment. Essentially, my roots are suffocating. They cannot breathe, and without oxygen, they cannot uptake the water and nutrients you are providing, no matter how generous you are. This initial stress weakens my entire system, making me vulnerable.
In this weakened, oxygen-starved state, I become an easy target for opportunistic soil-borne pathogens, most commonly fungi from the genera Pythium, Phytophthora, and Rhizoctonia. These organisms are often present in small, harmless numbers in the soil. However, the anaerobic, waterlogged conditions are their ideal breeding ground. They rapidly multiply and attack my compromised root system. They release enzymes that rot and break down my root cells, turning them from firm and white into a mushy, brown, and decaying mass.
As my root system is destroyed, my ability to function collapses. This internal crisis is what you see above the soil. The yellowing and browning of my leaves are a direct symptom of my inability to uptake water and nutrients, a condition you know as drought stress, ironically caused by too much water. I wilt not from thirst, but because my water-conducting tissues are rotten and blocked. My growth becomes stunted because I have no means to gather the building blocks for new cells. The decay you smell from the soil is the scent of my dying root tissues being consumed by the very pathogens that are killing me.
To understand the cure, you must understand my native needs. I am a Mediterranean herb, evolved for gritty, well-draining soil, full sun, and periods of dryness. My roots are built to seek moisture in rocky, free-draining earth. They are not adapted for constant dampness. Therefore, the single most important thing you can do for me is to emulate these conditions. Plant me in a sharply draining soil mix amended with sand, perlite, or grit. Ensure my pot has large, unblocked drainage holes. Most critically, water me only when the top inch of soil is completely dry to the touch. I would much prefer to be slightly underwatered than overwatered.
If you suspect root rot, you must act decisively. Gently remove me from my pot and carefully inspect my root ball. Healthy roots are firm and white or light tan. Rotten roots are soft, brown, black, and will likely fall apart. Using sterilized shears, you must prune away all the affected roots. Be ruthless; any remaining rot will spread. Then, repot me into fresh, sterile, well-draining soil and a clean pot. Do not fertilize me immediately, as my damaged roots cannot handle it. Place me in bright, indirect light to recover before returning to full sun. This process is my only chance for survival.
