Every fall and winter all the leaves of my plants turn yellow or brown. I lose most of the foliage. They get a lot of sun sitting or hanging on
The first thing to check is the temperature on your sun porch. Check it at night and during the day. If it is below 40 degrees at times, that is your problem. Most plants will not survive cold temperatures. Some plants do not do well when below 60 degrees. If the temperature is satisfactory, there may be cold drafts that occur when outside doors are opened. During the fall and winter the length of time the sun shines is reduced significantly and the weather is more often overcast than during the summer. Reduced light can cause plants to shut down and drop leaves.
In both cases it is necessary to move the plants to a warm window environment or under lights in a warmer site.