Moon Cactus

(Gymnocalycium mihanovichii)

What is the plant

It’s hard to mistake a moon cactus; you’ll always recognize them by their bright pink, yellow, or orange colors. The bright neon colors are usually in the shape of round looking balls, with thorns, and they’re sitting on top of another green colored cactus. The little moon cactus is a funny plant because it’s actually two plants in one and the product of human design.

Gymnocalycium mihanovichii is a handsome, miniature cactus native to South America that grows just 4-inches tall and 5-inches broad. They are nearly spherical, with 8-14 ribs, typically grey-green in color with burgundy accents, short, bristly spines and white tufted points. The vibrantly colored varieties all date back to a single nurseryman in Japan in 1940. Out of 10,000 grey-green Gymnocalycium seedlings, two showed some intriguing reddish coloring. His efforts to hybridize these seedlings for more brilliant coloring were wildly successful. Today, roughly 15 million grafted cactus are traded internationally — the vast majority of them moon cactus that have been developed and produced in South Korea.

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Planting

Popularity

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Container

Plants that don't like a lot of moisture will need a drainage hole for moisture to escape and for airflow to circulate through the pot. Another important function of drainage holes is to allow water to flush the soil of excess salts from fertilizers. Terracotta containers are a good choice for cactus gardens. They let water evaporate faster than other materials. Terracotta containers are a good choice for cactus gardens. They let water evaporate faster than other materials.

Water

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.

Soil

Mix together three parts potting soil, three parts coarse sand or gravel, and two parts perlite or pumice. Don't use a potting soil mix that contains fertilizers because the fertilizer can burn cacti roots and cause leggy growth.

Fertilizer

Most cacti and succulents don't need a specific blend. They grow healthy and happy when fed with a highly diluted all-purpose fertilizer. However, a low-nitrogen content, water-soluble fertilizer is best suited for the job. Use a 5-10-10 blend or 10-10-10 fertilizer diluted to 1/4th strength.

Propagation

Being that these cacti are grafted, they are not appropriate for propagation. If you are interested in learning how to graft cacti yourself, it is not difficult, and many species can be successfully grafted. To regraft a ruby ball cactus top, use a sharp knife sterilized with alcohol, cut the top off a seedling columnar cactus, and cut the scion from the old rootstock. You will see a circle of vascular tissue at the center of the stems of the scion and new rootstock. Press the plants together so the circles at least partially align. Put rubber bands over the scion and the bottom of the pot the rootstock is growing in, holding them together until the tissues grow together. On some older plants, the gymnocalycium on the top naturally sends out offsets that cluster like satellites around the larger plant. You can remove these and pot them separately as individual gymnocalycium, but it still needs the supporting green cacti, which supplies the plant its chlorophyll, if it does not have that, it will die. 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.

Temperature

The moon cactus calls for the temperature that you might expect for a desert type plant.

Sunlight

Grows it's best and fastest with full sun exposure, but it can do well in partial shade.

Pruning

Dead or dying sections of the plant can encourage pest infestation or disease. Removing these not only makes your houseplant look better, but reduces the risk of further problems down the line.