From my perspective, the most common reason my leaves turn brown is a simple lack of water. My roots are in the soil, and they can only absorb what is available to them. When the soil becomes too dry, my root system cannot transport vital moisture to my stems and leaves. The cells in my leaves begin to desiccate and die, starting at the tips and edges where water is hardest to deliver, resulting in that crispy, brown appearance you see. While I am drought-tolerant, my tolerance has limits, especially if I am in a small pot that dries out quickly under the hot sun.
Conversely, your kindness with the watering can can be just as deadly. My roots need oxygen as much as they need water. When I am sitting in constantly soggy, poorly-draining soil, my roots begin to suffocate and rot. This root rot means my underground parts are dying and can no longer absorb any water or nutrients, no matter how wet the soil is. This creates a cruel paradox where I exhibit the same brown, wilting leaves as when I am thirsty, but it is because my drowned roots have failed. This is often my fate in a pot without proper drainage holes.
I draw all my sustenance from the soil around me. If that soil is depleted of essential nutrients, I cannot perform basic functions to keep myself green and healthy. A lack of key elements like nitrogen can cause my older leaves to yellow and then turn brown as I try to move the limited nutrients to support new growth. On the other hand, an overabundance of fertilizer can be toxic. The high concentration of salts in chemical fertilizers can actually draw water out of my roots, effectively burning them and causing rapid browning and scorching of my foliage.
I am a Mediterranean plant, built for bright sun and warm, arid conditions. However, extreme or abrupt changes in my environment cause severe stress. Intense, reflected heat from a nearby wall or window can literally scorch my leaves, causing brown, brittle patches. While I love sun, a sudden move from indoors to full, blazing outdoor sun without a gradual adjustment period will shock my system, leading to sunscald. Furthermore, despite my hardy nature, a harsh, wet winter can cause die-back, where my extremities turn brown from the cold, damp conditions.
Sometimes, the browning is not directly from the elements but from tiny invaders. Pests like spider mites suck the sap directly from my leaves, puncturing the individual cells and draining my vitality. The damage they cause appears as tiny yellow stippling that eventually coalesces into larger brown, dead areas. If you look closely under my leaves, you might see their fine webbing. Other pests, like aphids, can cause similar stress and damage, leaving me weakened and susceptible to disease, which can also manifest as browning.
