How to tell
Overwatering & early root rot. The soil is still wet days after watering, the lower and oldest leaves yellow first, and the stem base may feel soft, often showing as yellowing leaves.
Thirst (underwatering). The soil is bone dry, and the yellowing arrives alongside crispy leaves rather than soft, mushy growth.
Too little light. The yellowing comes with pale, stretched new growth leaning toward the nearest window. That combination shows that the spot is too dim for Inch plant.
Hungry (nutrient shortfall). Older leaves fade to an even pale yellow and growth has clearly slowed, usually after many months in the same tired mix.
Simple old age. A single bottom leaf slowly yellows while the rest of the plant looks healthy and is pushing new growth.
