Answer: In many cases, leaf drop can be traced to overwatering. It's true that plants have to have water, but when maintained inside, the water needs of most plants isn't nearly as much as when growing outside on the porch or patio during the summer.
It's easy to determine if your plant's problem is related to overwatering. If the growing medium is soggy, the root system has a "sour" smell, and roots are dark and off-colored, the problem is most likely due to houseplant watering practices. You should be able to take a peek at the roots of larger plants by gently sliding the plant part way out of the container.
As a general rule, keeping the soil evenly moist will keep most houseplants happy, but do a little checking to find about your plant's specific water requirements. Avoid such practices as keeping a plant sitting in water in its saucer. Remember, too much of a good thing can spell disaster, particularly when it leads to root or stem rot.
Try letting the top of the soil dry out slightly before watering thoroughly. Sometimes you can tell if a plant needs water by simply lifting it up. If the pot feels light, it needs water; if the pot feels heavy, you can wait a few more days before watering.
Leaf drop can also be caused by overheating, or by sitting in cold drafts such as from an air conditioner.
A final observation - all the plants you mention grow in full sunshine outdoors. They may simply not be getting the sunshine they crave.
Hope this information helps you determine the cause of the leaf drop.
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