It looks like your geraniums are potted and on your deck. My guess is a deer or a rodent. I've had this happen with a groundhog, and sometimes squirrels or skunks will take a fancy to the flowers. My remedy has always been to elevate the plant on a stand so the groundhog can't reach it. I use two foot high terracotta chimney liners. For deer, there is no guarantee that any remedy will work. It depends on the deer and how acclimated to a landscape plant diet they are.