Gymnocalycium mihanovichii friedrichii is commonly known as 'Hibotan' or "Moon Cactus". This variant occurs when the plant lacks chlorophyll, and the body color manifests as beautiful pink, orange, yellow, or red rather than the typical green. It was discovered that these beautiful seedlings could not survive on their own since they did not have chlorophyll; therefore, they were incapable of producing the necessary chemical changes that are involved in photosynthesis and necessary for the production of the "food" that is essential for the plant to grow and thrive. It was determined that if these tiny seedlings were "grafted" (an actual physical union of the vascular systems of the two plants) onto fast growing plants, such as Hylocereus, the "base" plant could provide the necessary chlorophyll for the "upper" plant (in this case the Gymnocalycium seedling that lacked chlorophyll) to thrive.
"Moon Cactus" is an excellent subject for windowsill culture. It requires porous cactus soil with adequate drainage and prefers filtered light or shade with ample airflow. Water thoroughly when soil is dry to the touch and protect from frost.
Be careful not to over-water your plant; this can cause rotting of the root system, and your plant will die. On the other hand, don't allow the plant to dry out too much because this can cause the root system to collapse and become unable to take up water.
The general "Rule of Thumb" is: "When you water, water well." However, with succulent plants you must be careful to make sure the plant needs water. Feel the weight of the pot just after being watered and when it is dry. A totally dry pot weighs considerably less and is one sign of a thirsty plant. Feel the soil at least one inch down, and if the soil is dry, it is time to water the plant. Let the water thoroughly drain through the roots and out the bottom, making sure the entire pot of soil is saturated. Drain thoroughly; never let plants sit in water. Use a soil mix that drains well and allows some drying out between waterings. Top dressings, such as small pebbles or coarse gravel, offer quicker water penetration, slower water evaporation, elimination of a crust on the top of the soil, and a neat, attractive appearance. When plants are vigorously growing and blooming, they will need more water. During their non-growing or resting stage, usually in cold winter weather, they will need very little water.