Some leaf drop occurs when plants are subjected to a big change in environment. Such changes occur when plants grown outside for the summer are brought inside for the winter. Greenhouse grown plants may drop leaves if placed in dimly lit house conditions. Leaf drop brought on by a change in environment should last about 3 weeks then stop. A cause of leaf drop related to environment is that caused by chilling.
Tropical plants are sensitive to low, but above freezing, temperatures.
Plants on window sills may be exposed to chilling temperatures. Hot or cold drafts may be a problem to some plant. The prime example of a plant that drop leaves due to exposure to drafts is the poinsettia. Insects and diseases can cause leaf drop but they are not as common as the previously listed causes. Some leaf drop on house plants is normal.