Moon Cactus Care Guide: How to Grow a Moon Cactus

The moon cactus (Gymnocalycium mihanovichii) is a type of cactus native to South America’s deserts in Brazil, Argentina, and Paraguay. A member of the Cactaceae family, this succulent plant is also known by the common names ruby ball cactus, star flowered cactus, and red cap. At maturity, the moon cactus is approximately one to two inches wide and has clusters of small, sharp spines.

As houseplants, moon cacti are typically mutants that do not produce chlorophyll, which is why they have such vivid colors—from hot pink to neon yellow. Due to this lack of chlorophyll, they must be grafted onto a rootstock cactus to survive. The moon cactus is most commonly grafted with Hylocereus undatus (dragon fruit), but it can be combined with a green cactus of any species; Cereus peruvianus and Trichocereus spachianus are also common.

With proper care, these succulents will bloom vibrant flowers in late spring or early summer.

• Provide the appropriate balance of light and shade. The rootstock cactus must receive enough sunlight for photosynthesis. Position your moon cactus near a window, but ensure that it only receives partial sunlight, as bright light can be damaging. If you decide to place your cactus on a windowsill, ensure that blinds protect it from receiving too much direct sunlight.
• Plant your moon cactus in well-draining soil. Overwatering a moon cactus can lead to root rot or mealybugs. Potting soil mix for cacti is acceptable for moon cacti, or you can add perlite or coarse sand to the soil for improved drainage. Choose a porous clay pot with drainage holes to help excess water drain.
• Water your moon cactus sparingly. Like many species of cacti, the moon cactus does not require large amounts of water. When watering, thoroughly soak the soil, then allow it to dry out completely. Do not water the plant again until the soil has remained dry for approximately one week. The moon cactus should only be watered in the growing season and not in the winter months.
• Place your moon cactus in a warm environment. Choose a location where the temperature does not dip below 60 degrees Fahrenheit. You can keep a moon cactus outdoors during the warmer months of the year, but move it indoors during the winter as frost is fatal to this cactus plant.

The moon cactus is a grafted cactus and cannot propagate. Follow these steps to re-graft your moon cactus if you notice the top of your moon cactus separating from the rootstock cactus:

1. 1. Carefully remove the moon cactus. Using a sterilized knife, cut off the colorful top of the cactus.
2. 2. Trim the rootstock cactus. If you do not plan to use a new rootstock, cut off the old rootstock’s top layer.
3. 3. Bind the moon cactus and the rootstock cactus together. Place the moon cactus on top of the rootstock, and secure it firmly with rubber bands or twine around the entire cactus and pot. The two cacti will be bonded after approximately two weeks, at which point the rubber band or twine may be removed.

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