Ruby & Yellow Ball Cactus- This one is aptly named. There's a little red or ruby colored ball above a more familiar green cactus trunk We've got one of these pups in the LIB office. It's ideal for people who have neither the time, nor perhaps, the desire, to spend a lot of time watering. The main cause of death for this plant: Overwatering. And here's the kicker, it only needs the equivalent of 1 ice cube worth of water a month. And as for light, bright sun, to moderate light will work.