Most Ficus plants are susceptible to insect pests, such as scales and spider mites. When indoor trees lose leaves, one of these insects may be the culprit. Be sure to check your indoor Ficus plants regularly for signs of pest infestation. Another common cause of leaf loss on Ficus plants is environmental stress. indoor Ficus that are not getting enough light or proper humidity will experience leaf loss as a result of environmental stress.
In addition to these causes, indoor tree leaves can also fall off due to transplant shock, over-pruning, and lack of nutrients (especially during winter months when indoor gardeners often choose not to fertilize indoor trees).