Moon Cactus

Written by Em Casalena
Published: March 28, 2023
Share on:


For the succulent collector, there is practically no limit to the variety of cacti and succulents’ sizes, textures, colors, and forms. The moon cactus is one such cactus that is loved for its unique appearance. Due to the moon cactus plant’s unusual genetic makeup and inability to generate chlorophyll, it has to be grafted onto a rootstock in order to grow.

The growing instructions for this cactus are similar to those for other succulents. However, even with proper care, these plants only live for a limited time. We’ll explain all you need to know about the moon cactus in this article, including how to cultivate one (or more!) at home.

What is a Moon Cactus?

The moon cactus is botanically known as Gymnocalycium mihanovichii. It is a South American cactus species. The most well-known cultivars are different mutated specimens that have no chlorophyll at all, revealing the red, orange, or yellow coloring that exists in the absence of the green.

The combined plant is known as the moon cactus because these mutant strains are grafted onto the Hylocereus cactus. Moon cacti are also known as ruby balls, red Hibotans, or red caps. They are very popular indoor plants.

Anatomy of the Moon Cactus

The independent body of the moon cactus has a round, wide, and sometimes reddish overgrown cactus body with a diameter of around two inches. The typically eight ribs have sharp edges and a little notch. The six thorns are greyish-yellow, flimsy, and somewhat curled. The blooms of this cactus come in many different colors and are shaped like bells. Two rows of stamens with a light green hue are also present in this species. The stylus of this plant is usually light green or slightly yellowish. This species’ fruits have a spindle-like form.

Moon Cacti Native Environment

In Paraguay and northeast Argentina, this type of cactus can be found growing at lower elevations of up to 1,640 feet. Their natural environment is the desert, specifically across South America. Gymnocalycium plants can be found in over 70 different species in Bolivia, Brazil, Paraguay, and Argentina. This species was discovered in 1903.

Moon Cacti Varieties and Subspecies

Because the moon cactus is so varied, several different types have been identified. Since they lack chlorophyll and are unable to survive on their own roots, the species that make up the moon cactus cultivar have a different hue from the native one. This necessitates that they are grafted onto another Cactacea, usually Hylocereus specimens. The Filadelfiense moon cultivar is one lone variety that maintains a tiny size and has yellow branches.

The bright colors of the moon cactus, like this red and yellow plant, are stunning!

The bright colors of the moon cactus (pictured) are caused by a lack of chlorophyll.

©Yongkiet Jitwattanatam/

Colors of the Moon Cactus

The fact that moon cacti can be found in a variety of hues is one of its most delightful features. Moon cacti can be brightly colored purple, red, yellow, orange, or white. Older plants occasionally produce pink blossoms in the summer. Many people mistake the plant itself for a flower when they see the colored ball on top. However, moon cacti flowers grow separately from the grafted ball.

What Will Make My Moon Cactus Bloom?

Pink flowers will bloom on wild moon cacti in the spring, often in April or May. Although horticulturists have observed pink blooms on the deeper fuschia and purple varieties, the vibrantly-colored grafted cacti don’t usually blossom. When it comes to indoor plants, the flowers can occur throughout the year and can appear as a very faint pink to a vivid crimson.

As the lower rootstock and the grafted scion are two separate species with distinct blooming patterns, you could occasionally discover this plant producing two different kinds of blooms. Yet, if the plant bears no blooms at all, it is not a concern. This is a short-lived plant that will probably not bloom indoors.

The moon cactus occasionally produces buds, although these could disappear before the bloom fully unfolds. This is typically caused by either too little or too much water or by a recent environmental change, including increased sun exposure or a change in temperature.

Can Moon Cacti Be Propagated?

The bottom of the plant and the top of the rootstock cactus are often removed before the moon cactus is grafted and sold. The sliced edges of the two sections are secured together, and they rapidly heal together. Re-grafting this cactus onto a new rootstock will increase its lifespan. Moreover, this type of cactus can be grown from seed, although it will take at least a year to produce a usable specimen.

How to Grow a Moon Cactus

USDA hardiness zones 11 and 12 are suitable for growing the moon cactus outdoors. They often perform better indoors in regulated settings. Moon cacti are easier to cultivate if you have successfully grown succulents and cacti in the past. However, novice gardeners may have some luck with the moon cactus.

As mentioned earlier, this type of cactus lacks chlorophyll. As a result, it depends on the rootstock cactus for sustenance. The upper and lower parts of the plant are dependent on one another. If the demands of the scion on top and the host cactus on the bottom cannot coexist, one or both may perish.

These plants, like many cacti, enjoy a dry spell in between waterings, even to the point of mild wilting. That being said, you should water deeply when you do. The plant will visibly thicken up. This cactus shouldn’t be left in constantly wet soil or standing water because this might lead to the development of root rot. For optimal results, fertilize the cactus while it is still developing.

A yellow moon cactus growing on top of a green species on pebble stones in a garden.

Moon cacti (pictured) are easy to grow but only live for a few years due to being grafted.

© intarajinda

Repotting and Transplanting a Moon Cactus

While these plants don’t grow quickly, they should be replanted every three to four years to give them new life in new soil. Repotting ought to take place in the warm growing season. When repotting a cactus, make sure the soil is completely dry, and then carefully take the container off.

Be cautious to remove any rotting or dead roots when you remove the old dirt from the roots. Use a fungicide on any cuts. Spread the roots out as you repot the plant, then put it in its new container and cover it with succulent potting soil. To lessen the chance of root rot, let the plant go for about a week without any water, and then start watering it sparingly.

Pruning a Moon Cactus

Sharp pruners should be used to cut off any side shoots that the lower rootstock part may produce. Place them at the stem’s base for a fuller plant. Pruning is not required elsewhere.

Water Needs for Moon Cacti

Between waterings, let the soil mixture almost completely dry up before giving it a good soak. While keeping the plant in water for an extended period of time might cause root rot, good drainage is crucial.

This plant can require regular watering during the summer, especially if it has been relocated outside. Small-potted plants just require weekly watering. The moon cactus doesn’t need to be regularly misted in the winter.

Sunlight Needs for Moon Cacti

The ball tops of moon cacti don’t like direct sunshine and may tolerate more shade than many other cacti. The stock green cactus at the bottom, on the other hand, needs light. The optimal conditions for these cacti are areas with bright, indirect light and only a few hours of morning sunshine. The colors will fade if there is too much direct sunlight.

Soil Needs for Moon Cacti

The optimal cactus mix for this species has a low pH and is rich and quick-draining. Verify that the soil satisfies the requirements of the host cactus at the bottom as well.

Fertilizer Needs for Moon Cacti

This type of cactus plant does not require routine fertilization. But from April to September, when it is in bloom, you should give it a monthly dosage of cactus fertilizer. Feeding should be stopped during the wintertime dormant period.

Temperature and Humidity Needs for Moon Cacti

It’s possible that the ideal circumstances for the upper scion part and the rootstock of your moon cactus will be different. In USDA plant hardiness zones 11 through 12, the top scion is at its most resilient. The ideal temperature range in the winter is between 50 and 60 degrees F. Borderline temperatures have the potential to kill the top section while preserving the rootstock. This plant likes low humidity levels, like the majority of cacti.

Pests and Diseases to Watch Out For

The majority of common pests do not damage cacti in general. However, spider mites or mealybugs can harm indoor plants. Neem oil or a chemical pesticide made for cacti can be used to manage them.

The only disease that is relevant for this cactus is root rot, which is brought about either by overwatering or poorly draining soil. Withhold all water if the plant’s base starts to get mushy and squishy. You might be required to remove the old host cactus and regraft the top section onto a new one if the damage is severe.

In certain circumstances, you might notice that the color of your moon cactus is starting to fade. That generally happens when this type of cactus receives too much direct sunshine, which causes the pigmentation to wash away. This causes the bright red, yellow, or orange top section to fade. Place the plant in a spot that receives plenty of indirect light.

Ball detachment and collapse are additional issues for the moon cactus. The columnar lower host cactus may progressively collapse as a result of root rot. Again, this is usually brought on by overwatering. After a few years, the graft separates because the two cactus species develop at different rates. The best course of action at this time is to cut off the top section and graft it onto a different rootstock cactus.

Is It Hard to Grow a Moon Cactus?

Not at all! It is an easy cactus to grow and manage. However, because of its short lifespan, this species is avoided by many collectors. Moon cacti are short-lived because they are grafted. Your moon cactus should thrive for a few years, maybe longer. But, eventually, the two grafted plants will start to separate or divide. Unless this type of cactus is grafted onto a new foundation, it will perish. Keep this in mind when making a decision to buy this type of cactus.

The moon cactus is a unique delight among desert plant collectors. It’s quite fortunate that this species is so easy to care for as well!

The photo featured at the top of this post is © Kanjana Wattanakungchai/

Share on:
About the Author

Em Casalena is a writer at A-Z Animals where their primary focus is on plants, gardening, and sustainability. Em has been writing and researching about plants for nearly a decade and is a proud Southwest Institute of Healing Arts graduate and certified Urban Farming instructor. Em is a resident of Arizona and enjoys learning about eco-conscious living, thrifting at local shops, and caring for their Siamese cat Vladimir.

Thank you for reading! Have some feedback for us? Contact the AZ Animals editorial team.