My Diffenbachia leaves curl up from time to time. I water it once a week and it gets moderate sunlight. It opens back up eventually. Can anyone explain why this happens?
It may be the sunlight- this plant tolerates dappled sunlight or shade, so if 'moderate sun' means direct sunlight, find another position for it. Water shortage doesn't usually cause leaves to roll up, merely to flop, but you should water when the surface of the soil feels just about dry to the touch and water thoroughly. Note that new leaves start out rolled up and gradually open as the days go by, but once open, they don't roll up again.