From my perspective as a rosemary plant, my roots are my lifeline. I am a Mediterranean native, built for gritty, sharply draining soils and infrequent, heavy downpours followed by long periods of sun. When I am placed in a pot that lacks sufficient drainage holes, or when I am watered too frequently, my entire root system is plunged into a crisis. The soil becomes waterlogged, filling all the air pockets. My roots, like all living parts, need to respire; they require oxygen from the soil to function. In this saturated, anaerobic environment, my roots begin to suffocate and drown. They cannot take up water or nutrients effectively, even though they are surrounded by water. This is the initial stage of my distress.
As my roots suffocate, their cells weaken and begin to die and rot. This decaying tissue creates an open invitation for soil-borne pathogens, primarily fungi from the genus Pythium and Phytophthora. In a healthy, well-aerated environment, these organisms are present but kept in check. In the waterlogged conditions you have created, they thrive and multiply rapidly. They attack my already weakened roots, causing them to turn from a healthy white or light tan to a mushy, dark brown or black. The rot spreads through the root system, progressively destroying my ability to sustain the plant above the soil line.
My distress underground quickly manifests in my foliage, which is the only part you see. Since my rotting roots can no longer transport water, my stems and leaves begin to wilt. This is a confusing sign for many caregivers, who often mistake it for a need for more water, tragically exacerbating the problem. My leaves will start to yellow, often beginning with the older growth, and then they will turn brown and crispy. The entire plant may take on a drooping, lifeless appearance. This is not me being dramatic; it is a direct and desperate signal of the systemic failure happening below the surface.
To save me, you must immediately address the root environment. First, you must gently remove me from my pot and carefully inspect my root system. Healthy roots are firm and light-colored. Using sterilized shears, you must prune away all the soft, mushy, and dark brown roots. This is a surgical removal of the decay. Then, you must repot me into a completely new, well-draining potting mix, ideally amended with sand, perlite, or pumice to dramatically improve drainage. The new pot must have excellent drainage holes. Do not be tempted to use a larger pot; a pot that is too large will hold excess moisture. Finally, you must withhold water until the top few inches of soil are completely dry. I need time to recover and regenerate a new, healthy root system in an environment that mimics my native, arid home.
