From my perspective, water is life, but it is also a source of great stress. My roots are designed to seek out moisture, but they also need to breathe. When you provide me with too much water, the soil becomes saturated, pushing out the air. My roots begin to suffocate and rot in this waterlogged environment. Once they are damaged, they can no longer effectively transport water and nutrients to my leaves. This causes the cells in the leaf tissue to die, starting from the tips or edges, and manifesting as those soft, dark brown, mushy spots you see. Conversely, if you allow my soil to become bone dry, I become severely dehydrated. The soil can actually become hydrophobic, repelling water away from my roots. Without adequate moisture, the leaf tissues desiccate and die, resulting in crispy, light brown spots, often starting at the edges.
I hail from the warm, humid tropics, and my large, broad leaves are adapted to that environment. The air in most homes, especially during winter when heating systems run, is extremely dry from my point of view. This low humidity causes rapid moisture loss from my leaves through transpiration. If the rate of water loss from my leaves is greater than the rate of uptake by my roots, the leaf edges and tips will dry out and turn brown first. Similarly, I am sensitive to sudden drafts of hot or cold air. Being placed near a heating vent, an air conditioner, or a frequently opened door subjects me to temperature stress, which can also damage my cells and cause localized browning.
While I am not a heavy feeder, I do require a balanced diet to maintain my vibrant green foliage. A lack of essential nutrients, particularly nitrogen or magnesium, can cause a general chlorosis (yellowing) that may be accompanied by spotting. More commonly, an excess of certain minerals, specifically from over-fertilization, can be the true culprit. A buildup of soluble salts from fertilizer in the soil can actually draw water out of my roots—a process called reverse osmosis. This "chemical burn" damages my root system, leading to poor water uptake and subsequently, brown, scorched-looking spots on my leaves, particularly at the margins.
Though I am resilient, I am not invincible to attack. Tiny pests like spider mites, scale, and mealybugs see my succulent leaves as a source of food. They pierce my epidermis and suck the sap directly from my cells. This feeding activity physically damages the tissue and robs me of vital nutrients. The initial damage often appears as small, yellow speckles. As the feeding continues and the injury worsens, these spots can coalesce and turn brown as the cells die. You may also notice a sticky residue (honeydew) on the leaves or a fine webbing if spider mites are present.
Not every brown leaf is a cause for alarm. Like all living things, I go through a natural life cycle. It is perfectly normal for my oldest, lowest leaves to eventually yellow and develop brown spots before they fully senesce (age and die) and fall off. This is simply my way of reallocating my energy and resources to producing new, healthy growth at the top of my stem. As long as this is happening gradually and only to the lower, mature leaves while the rest of my foliage remains robust and green, it is a natural process and not a sign of distress.
