Assuming you are referring to the plant known as Epiphyllum anguliger, commonly called fishbone cactus or zigzag cactus, here are some tips on watering. As with most cacti, this plant is adapted to survive long periods without water. They will do best if allowed to dry out completely between watering. Water fishbone cacti deeply but infrequently, about every 2-3 weeks during the growing season and even less often in winter. Be sure to drain any excess water from the saucer after each watering. Overwatering is the most common cause of death for these plants.