From my roots' perspective, the most common reason my leaves turn crisp and brown is a simple lack of water. I am a Mediterranean plant, yes, adapted to sunny, dry climates, but that does not mean I can survive on mere sips of water. My extensive root system seeks moisture deep in the ground. When I am confined to a pot or a new planting, my access to water is limited. If the soil around me becomes too dry for too long, my delicate root hairs shrivel and die. Without these tiny roots, I cannot drink, and the water transport system within my stems fails. The moisture cannot reach my leaves, and they desiccate, turning from green to a dry, brittle brown, often starting at the tips. It is a slow, thirsty demise.
Conversely, your kindness with the watering can may also be my undoing. My roots demand oxygen as much as they demand water. When I am left sitting in heavy, soggy, or poorly-draining soil, water fills the air pockets between the soil particles. My roots begin to suffocate and cannot function properly. In this weakened, oxygen-starved state, they become susceptible to attack from soil-borne fungi, leading to a condition you call root rot. As my root system decays underground, it can no longer absorb water or nutrients. The paradox is that the symptoms above the soil mirror those of underwatering: my leaves turn yellow and then brown as I essentially die of thirst while standing in water. This browning is often more widespread and the stems may feel soft.
If I have been living in the same container for many seasons, my roots may have exhausted the available space and nutrients. They become a dense, tangled mass that struggles to absorb water and fertilizer effectively, even if you provide it generously. This stress manifests in my foliage. The older leaves, in particular, will begin to yellow and then turn brown as I am unable to sustain them. My growth will likely be stunted, and I will look generally unhappy. My pot has become a prison, and I am slowly starving within it.
While I am a hardy soul, a sudden hard frost or consistently freezing temperatures can cause severe damage. The water within the cells of my leaves can freeze, rupturing the cell walls and killing the tissue. This damage appears as a generalized browning or blackening of the leaves, often on one side of the plant that faced the prevailing wind or cold. Furthermore, on sunny winter days, my foliage may lose moisture through transpiration, but if the ground is frozen, my roots cannot draw up water to replace it. This leads to winter desiccation, another form of browning from thirst imposed by the cold.
Though I am naturally aromatic and somewhat pest-resistant, I am not invincible. Sap-sucking pests like spider mites can infest my leaves, especially in hot, dry, dusty conditions. They pierce my cells and drain their contents, leaving behind stippled, yellowing foliage that eventually turns brown and drops. Similarly, fungal diseases, often exacerbated by humid conditions and poor air circulation, can cause patches of browning or black spot on my leaves. These are less common issues for me but can occur when I am already weakened by other stresses.
