How to Grow Moon Cactus
If you can grow cacti and succulents successfully, you can likely grow the ruby ball cactus without too much trouble. These plants are popular in cactus dish gardens.
The ruby ball is an albino plant, it has no chlorophyll, therefore it relies on the rootstock cactus as a food source. It has a parasitic relationship. If there is a disconnect between the requirements of cactus on the bottom and the scion on top, one or both may die.
The red ball tops are tolerant of more shade than many cacti and dislike direct sunlight. By contrast, the stock green cacti on the bottom are often light-lovers. Look for a bright area, but not so bright that the color of the top begins to wash out.
A rich, fast-draining cactus mix with a low pH is ideal. Make sure you meet the soil needs of the host cactus on the bottom.
Allow the soil mix to become nearly dry between waterings, but then water thoroughly. The cactus should not be sitting in a marshy soil for more than a day or so, good drainage is essential. During the summer months, the plant may need frequent watering. Plants in small pots will only need weekly watering. Watering in the winter months is unnecessary, but mist occasionally.
Temperature and Humidity
The ruby ball scion is hardy in United States Department of Agriculture plant hardiness zones 11 through 12. Some of its rootstock (like night-blooming cereus or blue myrtle) is hardy in zones as low as 8 or 9. If the ruby red is grafted onto a plant that remains hardy in those lower temperatures.
You do not need to regularly fertilize your ruby ball cactus plant, but you should dose it with a cactus fertilizer every month during its growing season (April to September). Suspend feeding during the dormant winter period.
Potting and Repotting
Repot as needed, preferably during the warm season. To repot a cactus, make sure the soil is dry before repotting and then gently remove the pot. Knock away the old soil from the roots, making sure to remove any rotted or dead roots in the process. Treat any cuts with a fungicide. Place the plant in its new pot and backfill with potting soil, spreading the roots out as you repot. Leave the plant dry for a week or so to reduce the risk of root rot and then begin to water lightly.