Spiral Cactus Care and Potting Instructions: Soil: Use a pot with a drainage hole and fill it with a cactus potting mix. The type of soil that a cactus needs is a well-draining and extremely porous mix. It has to drain very quickly, so it doesnt hold onto too much moisture, and it should dry out within a day or two. Water: In spring and summer water weekly, in autumn and winter water every three to four weeks. Only water the plant when the soil is completely dry, or else the spiral cactus can become waterlogged and begin to rot. Fertilizer: Cereus forbesii does not require fertilization, however a boost of nutrients during the growing season will help them thrive.