But I wanted to eat some celery+peanut butter, and you can't spread peanut butter on a droopy celery stalk!
Laura had a great idea: stick the celery stalks in a glass of water and wait an hour or so
Sure enough, after an hour, the celery was as crispy as ever before! crunchy YUM!
The celery gets droopy because the plant cells get dehydrated in the refrigerator and start to loose all their water. When you soak the stalk in a glass of water, the water creeps back into the cells through osmosis. This swells the cell and stiffens the cell walls, making the celery stalk into a rigid, crispy structure.
This trick would probably also work on radishes and carrots and other vegetably things.