Hello, it is I, your Begonia. I am communicating not with words, but through my physical state. My leaves are my language, and their dropping is my cry for help. It is a sign that my fundamental needs are not being met in my current environment. Let me explain the most common reasons from my perspective.
My roots are very sensitive. They despise sitting in saturated, waterlogged soil as much as they fear becoming bone dry. When you overwater me, the soil pushes out all the air, and my roots begin to suffocate and rot. Once this rot sets in, they can no longer transport water and nutrients to my stems and leaves, so my leaves turn yellow, become soft, and drop off. Conversely, if you forget to water me, I become severely dehydrated. My leaves will first wilt and then become crispy and brown before falling, as I must sacrifice them to conserve the little water I have left for my core survival.
I am a creature of habit and despise sudden change. If you recently brought me home from the nursery or moved me to a new spot, I am likely experiencing transplant shock. The change in light, temperature, and humidity is a significant stressor, and I may drop leaves in protest as I focus my energy on acclimating to my new conditions. Furthermore, I am highly sensitive to drafts. A constant blast of cold air from an air conditioner in summer or a hot, dry gust from a heating vent in winter will cause me immense stress, leading to rapid and sudden leaf drop.
In the wild, many of my Begonia cousins thrive in the humid understory of tropical forests. My leaves are adapted to moisture in the air. When placed in the typical dry air of a modern home, especially during winter, the moisture evaporates from my leaf surfaces faster than my roots can replace it. This causes the leaf edges to turn dry and brown (a condition you call leaf scorch) and eventually, the entire leaf may become crispy and drop. I am not a cactus; I crave that moist, tropical breath.
Sometimes, my leaf drop is not your fault directly, but a sign of a secondary issue. Pests such as spider mites, mealybugs, or fungus gnats can infest my soil or feed on my sap. These tiny invaders weaken me significantly, disrupting my ability to function and causing my leaves to yellow, curl, and fall. Similarly, a fungal disease like powdery mildew or the root rot mentioned earlier can attack my system. These diseases block my vascular tissues and cause decay, forcing me to shed my compromised parts.
