From the perspective of the plant itself, the appearance of brown leaves on a *Ficus elastica* (Rubber Fig) is a visible symptom of internal distress. It is the plant's physiological response to suboptimal conditions that disrupt its vital processes. The primary causes can be broken down as follows.
This is the most frequent source of stress. The plant's roots require a specific balance of water and air within the soil pores. Overwatering saturates the soil, filling these air pockets and suffocating the roots. Without oxygen, the roots cannot respire or function, leading to root rot. As the root system fails, it can no longer transport water and nutrients to the leaves, causing them to turn soft, mushy, and brown, often starting at the lower leaves and the center of the leaf. Conversely, Underwatering causes a different kind of drought stress. The plant loses water through transpiration from its large leaves faster than the roots can replace it. To conserve resources, the plant will sacrifice tissue, resulting in dry, crispy brown patches, typically starting at the leaf edges and tips before spreading inward.
Native to humid tropical forests, the Rubber Fig's leaves are adapted to moisture-rich air. In a typical dry home environment, especially near heating or cooling vents, the rate of transpiration accelerates dramatically. The plant loses water vapor through its stomata faster than its roots can absorb it. This creates an internal water deficit, even if the soil is adequately moist. The leaf margins and tips, which are the furthest points from the veins, are the first to desiccate and die, resulting in characteristic dry, brown edges. This is the plant's direct response to an atmosphere that does not match its evolutionary needs.
Light is the fundamental energy source for photosynthesis. Too much direct, intense sunlight acts like a radiation burn on the leaf's delicate photosynthetic machinery (chloroplasts). It causes photoinhibition, damaging cells and leading to scorched, brown, crispy patches on the areas most exposed to the sun. Insufficient light is equally detrimental. In deep shade, the plant cannot produce enough photosynthetic energy (sugars) to sustain all its foliage. To redirect energy to new growth, the plant will systematically abort its oldest, least efficient leaves, often causing them to yellow and then turn brown before dropping. This is a strategic resource allocation response.
The plant's root system functions through osmosis, carefully balancing mineral uptake. Over-fertilization or watering with hard water introduces an excessive concentration of soluble salts (like sodium, chloride, and fluoride) into the soil. This creates a hypertonic environment around the roots, making it difficult for the plant to absorb water effectively—a form of physiological drought. Furthermore, certain minerals can become toxic at high levels, causing direct cellular damage. The plant often exhibits this stress as browning, particularly on the leaf tips and margins, as salts accumulate there after being transported in the water stream.
