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 three weeks then stop. Chilling is one cause of leaf drop related to environment.
Tropical plants are sensitive to low, but above freezing, temperatures.
Plants on windowsills may be exposed to chilling temperatures. Hot or cold drafts may be a problem for some plants. The poinsettia is a prime example of a plant that drops leaves due to exposure to drafts. Insects and diseases can cause leaf drop but are not as common as the previously listed causes. Some leaf drop on houseplants is normal.