Moon Cacti - Ruby Ball Cacti (Gymnocalycium)

Base plant (Root Stock): Selenicereus undatus. Top Plant (Scion): Gymnocalycium mihanovichii 


  1. Top Tips
  2. Location, Water, Humidity & Fertilisation
  3. Common Issues
  4. Origins, Temperature, Propagation, Repotting & Toxicity.

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Top Tips & Info

  • Care Difficulty - Easy
  • Moon Cacti will prefer a location that offers bright, indirect light at the very least, with areas that promote an hour or two of morning sunlight being the optimum. Avoid shady rooms at all costs due to the heightened chance of developing root rot.
  • Infrequently irrigate the soil with the mentality of 'Drenches Between Droughts'. Over-watering and too low light are the two most common problems amongst owners, so always allow it to dry out in between waters thoroughly.
  • Fertilise every two months using either a 'Cactus' or 'Houseplant' labelled feed. 
  • Repot every three to four years during the spring, using a 'Cactus & Succulent' labelled potting mix. If the two plants become separate, you can individually repot them both into their own pots with fresh soil. 

How Does This Plant Grow?

The Moon Cactus is two plants that have been grafted together to make this display. The bottom 'rootstock' is called Selenicerus undatus (the Dragonfruit Plant) with the coloured top ('scion') being a Gymnocalycium mihanovichii that has been joined together via horticultural grafting.

As both of these plants are from different climates, they also have different growth rates. The grafted union may come undone after a few years when the bottom plant (the Dragon Fruit) begins to enter its growing season. Don't worry though, as you can plant both plants into a 7cm pot of 'Cactus & Succulent' labelled potting mix to root on their own.

Location & Light - 🔸🔸🔸

Moon Cacti like to be seated in a bright location with a splash of morning or evening sun. Remember not to over-expose your specimen to the rays though, as it still may result in sun-scorch and dehydration. We'd recommend placing it on an east or west-facing window, or somewhere that boasts bright indirect light at the very minimum. The greatest amount of sunlight for this plant is around four hours per day.

Water - 🔸

These specimens are an excellent choice for those who frequently under-water their houseplants. Allow ALL of the soil to dry out in between waters, avoiding the use of too cold water if possible for maximum root growth. Under-watering symptoms include a shrivelled stem, yellowing leaves, little to no growth and dry, crispy patches forming on the leaf edges. These issues are usually caused by too much light/heat or forgetfulness; remember, the brighter the location, the more watering you'll need to do. Over-watering symptoms include a weakened or rotten stem, no new growth, yellowing lower leaves and eventual plant death. The differences between under and over-watering can be very similar, with a rotten base being the obvious difference. 

Humidity -

This is not a necessity; however, a quick hose down from time to time will hydrate the leaves and wash away dust or potential pests.

Fertilisation - 🔸

Supplement every two months using either a 'Cactus & Succulent' or a 'Houseplant' labelled fertiliser. As Gymnocalycium and Dragonfruit both naturally grow in nutrient-leached arid soils, forgetfulness won't be detrimental to their overall health. Never directly apply a 'ready-to-use' (RTU) without a pre-water first as this may lead to the burning or roots.

Common Issues with Moon Cacti

If the coloured top begins to brown and rot, it's most likely to do with too saturated soil or waterlogged conditions. Take the plant out of the pot and inspect the roots as they'll tell a lot about the plant's wellbeing. If the roots sport a yellow tinge, you're good to go, but if they're brown and mushy, action must be taken immediately. If the base of the plant (the Dragonfruit) begins to rot as well, discard the whole specimen. Alternatively, if only the base begins to rot, remove the scion (coloured top) and place it a quarter into a fresh batch of 'Cactus & Succulent' labelled compost. Keep the soil mostly saturated for the first month, before following the phrase 'drenches between droughts' again. Discard the base as it'll only spread across the whole plant.

In some cases, the scion will lose its colour. If the whole specimen doesn't show signs of rot and you know for sure that it isn't over-watered, don't worry too much. If, however, the base begins to brown over, scroll to the paragraph above for more information about this!

Curled leaves and dried brown edges are the result of too little water and over-exposure to the sun. Although they can naturally do well in sun-filled locations, those that haven't acclimatised to the harsh rays will show signs of sun-scorch and environmental shock. Prolonged exposure will significantly speed the process of dehydration, so consider transplantation into a bigger pot in the spring to wrap the roots around moister soil.

In some cases, the base plant will produce a lateral growth that can be propagated once it reaches the same length. Scroll down to 'Propagation' to learn more. 

Never allow temperatures to dip below 12ºC (54ºF) as irreversible damage may occur in the likes of yellowed foliage and weakened growth. If this happens, remove the severely affected areas and immediately improve growing conditions - never cut through softened yellow growth, and only around brown, crispy squares. As rehabilitation can take several months because of its slow-growing nature, be sure to provide a stable location with better growing conditions to speed this process.

Mould or mushrooms developing on the soil means two things - too little light and over-watering. Despite the harmlessness, it'll prove unsightly to most gardeners and is therefore removed once known. To remove, replace the top two inches of the soil for a fresh batch of 'Cactus & Succulent' compost. Either increase the amount of light received (no direct sunlight for the first few weeks to prevent environmental shock) or decrease the frequency of waters slightly. If the mould is accompanied by yellowing lower leaves, you may also have a case of root rot.


As this product is two separate species grafted together, it's origins are slightly different. Unfortunately, there isn't too much information on when it was first commercialised, so this section will only be mentioning the two species' taxonomic history.

Gymnocalycium mihanovichii was initially documented as 'Echinocactus mihanovichii' in 1905 by Frič & Gürke, before being shifted in the current genus seventeen years later. Britton & Rose acknowledged the species' name, which honoured botanist Nicolas Mihanovich, but placed it within the Gymnocalycium genus after documentation and research.

The rootstock plant's original name, Hylocereus is an epiphytic or lithophytic genus originating from Central America. It was first described by Britton & Rose in the early 20th century, using the Greek and Latin words hyle, meaning wood, and cereus, referring to its 'waxy' nature. The current name of the species, Selenicereus undatus, also originates from Latin, with the first section translating to 'moon' (Selḗnē) in reference to its appearance. The species epithet, undatus, translates to 'wavy edges' which refers to the rib-like structure of the stem.

The Distribution of Gymnocalycium mihanovichii in Red & Selenicereus undatus (Dragonfruits) in Green.


15° - 32℃   (59° - 90℉)
H1a  (Hardiness Zone 12)  - Can be grown outdoors during the spring and summer in a sheltered location whilst nighttime temperatures are above 15℃  (59℉),  but is fine to remain indoors, too. If you decide to bring this plant outdoors, don't allow it to endure more than three hours of direct sunlight a day as it may result in sun-scorch. Regularly keep an eye out for pests, especially when re-introducing it back indoors.


The individual rates of both species' growth are much different when kept separately in their own pots, but as a 'duo', their rates will be almost nil. Generally, the rootstock (Dragonfruit) may produce lateral branches over time, which can be propagated via the link of the 'Propagation' section.

Pruning & Maintenance

Remove yellow or dying leaves, and plant debris to encourage better-growing conditions. While pruning, always use clean scissors or shears to reduce the chance of bacterial and fungal diseases. Never cut through yellowed tissue as this may cause further damage in the likes of diseases or bacterial infections. Remember to make clean incisions as too-damaged wounds may shock the plant, causing weakened growth and a decline in health.

If either of the two species is beginning to rot, scroll up to 'Common Issues' for more information on removing or separating them!


Only the rootstock (Dragonfruit) can be propagated successfully if it produces a lateral branch (Stem Cuttings). Click here and scroll to 'Propagation' to learn more.


This product won't flower in its lifetime; however, the species (when individually grown) may flower once they hit maturity of a few years. Gymnocalycium mihanovichii will product several small pinky-white flowers in the late winter across the top half of its 'crown', whereas the Dragonfruit's flower is rather large and sweetly-scented.


Repot every three to four years in the spring using a 'Cactus & Succulent' labelled potting mix and the next sized pot with adequate drainage. Moon Cacti are far better potbound for several years due to the heightened risk of root rot and repotting-issues (like transplant shock) - so only repot if you feel it's wholly necessary.

Hydrate the plant 24hrs before tinkering with the roots to prevent the risk of transplant shock. For those situated in a darker location, introduce extra amounts of perlite and grit into the lower portion of the new soil to downplay over-watering risks. Click here for a detailed step-by-step guide on transplantation, or via this link to learn about repotting with root rot.

Book a 1-to-1 video call with Joe Bagley if you'd like a personal guide to repotting your houseplant. This will include recommending the right branded-compost and pot size, followed by a live video call whilst you transplant the specimen for step-by-step guidance and answer any further questions!

Pests & Diseases

Keep an eye out for mealybugs, scale & root rot, although Moon Cacti are usually pest-free. Common diseases associated with Moon Cacti are root rot, leaf-spot disease, botrytis, rust, powdery mildew & southern blight - click here to learn more about these issues.


This plant is slightly poisonous. If parts of the plants are eaten, vomiting, nausea and a loss of appetite could occur. Consumption of large quantities must be dealt with quickly; acquire medical assistance for further information.

Retail Locations

Some Garden Centres & Online.

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