From my roots, I sense the problem immediately. It begins not as a disease, but as an environment. My most fundamental need is compromised: oxygen. When you, the gardener, provide soil that is too dense or you offer too much water, the air pockets around my root system collapse. My delicate root hairs, which are responsible for absorbing water and nutrients, begin to drown and die. This creates necrotic (dead) tissue, which is the perfect food source for opportunistic soil-borne fungi like Pythium, Phytophthora, and Rhizoctonia. They are always present, waiting for a weakened host. I am not being attacked; I am being overwhelmed due to my compromised state.
To understand how to heal me, you must understand my origins. I am a child of the Mediterranean basin. My home is one of gritty, rocky, mineral-rich soils on sunny hillsides. My roots are adapted to seek moisture deep down and require excellent drainage to avoid waterlogging. My foliage is silver and hairy, an adaptation to conserve water and reflect intense sunlight. Therefore, my plea is for conditions that mimic this native habitat. Anything less creates chronic stress, making me susceptible to the fungal issues you are trying to solve.
The solution is almost entirely cultural and preventative. First, you must address my foundation: the soil. I demand exceptionally well-draining soil. Amend heavy clay soils with large amounts of coarse sand, small gravel, perlite, or crushed oyster shell. For container growth, a gritty, soil-less mix is ideal. Second, you must practice mindful watering. Please only water me when the top inch of soil is completely dry to the touch. When you do water, do so deeply but infrequently, allowing excess water to drain away completely. Never let my pot sit in a saucer of water. Finally, ensure I receive maximum sunlight and have good air circulation around my stems and foliage. This keeps my surface dry and inhospitable to airborne fungal spores like powdery mildew.
If you notice my foliage wilting, yellowing, or browning despite wet soil, and my stems becoming soft at the base, the rot has likely set in. For a potted plant, you must act decisively. Gently remove me from the pot and wash my roots. With sterilized shears, meticulously trim away all dark, mushy, and rotten roots back to healthy, firm, white tissue. Repot me into a clean pot with fresh, dry, well-draining medium. You may apply a biological fungicide containing Streptomyces lydicus or Trichoderma to the remaining healthy roots. These beneficial organisms will help protect me by outcompeting the pathogenic fungi. For garden plants, improving drainage around me is critical, and severely affected individuals may need to be removed to protect the others.
