Grow the starfish cactus in a pot so you can bring it indoors during cool weather.
Pot the starfish cactus in a mixture of equal parts of potting soil and sand, or use a commercial succulent potting mix.
Keep the potted starfish cactus in an area where it won't receive direct sun. Placing it outdoors in the shade of a taller tree is ideal when the weather is mild. Experiment with different light levels, if the plant is kept indoors, until you find the ideal situation.
Water the starfish cactus just enough to keep it from dying. The plant, as with most succulents, is susceptible to root rot, and too much water may kill it. Keep an eye on the starfish cactus, and if you notice the stems beginning to pucker or shrink, water the plant thoroughly. Watch it more closely during hot weather.