Answer: Your plants are probably reacting to the change in temperature, humidity, and light indoors. It's natural for geraniums to lose the older leaves, and they usually yellow and fall off. But in this case, if the whole plant is affected, it's probably because of the change in environment. You can lessen this by gradually bringing your plants indoors, beginning with taking them in at night and back out again during the day, keeping them in for longer and longer periods of time, until they're eventually indoors 24 hours a day.
Now that your plants are indoors, you can pinch back the stems and new foliage will develop. If all conditions are right, including bright light or direct sunlight, they may even bloom for you this winter!
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