Moon cacti are one of the most commonly found cacti and are available in both small plant boutiques and grocery stores. Their labels often stress how easy they are to care for and how little they require. What their labels don’t tell you is that your moon cactus’ death is inevitable because it wasn’t designed to survive for long.

This post will explain why that is and what you can do about it because there IS something you can do!

Table of Contents

What is a moon cactus?
—- What is the top section?
—- What is the bottom section?
Why is this cactus not destined to survive long?
Can I save it?
—- Has your moon cactus been overwatered?
—- Saving the Rootstock
—- Saving the Scion
—- An Alternative Option to Saving the Scion – Buying a Chin Cactus
What happened when I tried to save mine

What is a moon cactus?

A moon cactus (Gymnocalycium mihanovichii) is also known as a hibotan cactus. It is actually two different species of cacti that have been grafted together.

Grafting means to join the tissues of two species of plants so that they will continue to grow together.

The top section of the moon cactus (the brightly-colored ball) contains no chlorophyll and therefore lacks the ability to produce its own food.

Because it cannot produce its own food, the top section would not be able to survive on its own. It uses the food-making capabilities of the lower cactus to thrive and survive.

What is the top cactus (scion)?

The top cactus is a Gymnocalycium mihanovicii friedrichii, sometimes referred to as a chin cactus.

When people or companies are producing these cacti, they refer to the ball cacti on top as the scion.

The scion is a young piece of plant used for grafting.

What is the bottom cactus (rootstock)?

The bottom cactus is a Hylocereus undatus, sometimes referred to as a pitahaya or dragon fruit.

When moon cacti are being produced, the bottom cactus is referred to as the rootstock supporting the scion.

The rootstock is the plant that a scion is grafted onto.

Why is this cactus not destined to survive long?

One of my own moon cacti that, once it showed signs of illness, quickly declined and perished.
The rest of the plants are still alive and well from this arrangement
.

The moon cactus cannot survive long because the scion functions as a parasite on the rootstock.

The rootstock is unable to produce enough food to sustain itself and the scion indefinitely.

So overtime the rootstock weakens from lack of nourishment trying to support both of them and begins to die, eventually leading to the death of both cacti.

How long will moon cactus live?

This is tricky to answer because we don’t know how long they were alive before we purchased them. It seems to be common for people to have moon cacti in the range of 1.5 to 3 years before they start to see a decline in health and then an eventual death.

Deaths due to overwatering and/or lack of light generally happen faster than this, which may help to determine what is causing ill health with your cactus.

Can I save it?

Yes! You have the ability to save both cacti to some degree if they are in good health. Good health is defined as not mushy, still firm, not super brown or discolored.

First, we will check whether your cactus has been overwatered and then we will cover what can be done for each part of your cactus to save it.

If you know you haven’t overwatered your cactus, you can skip to another section by clicking one of these options:
Saving the Rootstock
Saving the Scion
An Alternative Option to Saving the Scion

Remember, it is very possible (especially if you have had your moon cactus for some time) that your moon cactus is dying because it isn’t designed to live for long. It may have nothing to do with your care. You may have given it perfect conditions!

Has your moon cactus been overwatered?

How do you know if your moon cactus has been overwatered?

If more than one of these are true, your cactus might have been overwatered:

  • Your rootstock is turning brown or becoming mushy
  • The soil is wet and soggy but you did not just water your cactus within the last 24 hours
  • You check the roots of the cactus and they are brown or black and mushy
  • The cactus does not have a well-draining soil
  • You have been watering before allowing the soil to completely dry out first

If you have any of these signs, it would be a good idea (if you haven’t already) to check the roots for signs of root rot (brown or black, mushy roots).

If your cactus has root rot, click here to find out what to do!

For cacti suffering root rot, if the rootstock is mushy, there is nothing that can be done to save the rootstock. If the scion is firm and healthy, you could skip to the section to learn how to graft the scion onto a new rootstock.

If the rootstock is not mushy, but the roots have rotted, you do have an option. You will want to:
1. Cut off all brown or black mushy roots and only keep the white, healthy roots.
2. Then replant in well-draining soil and do not water your plant for at least a couple weeks.
3. When you do water, do not water again until the soil has dried out completely.

If the roots are still white and healthy, then planting in well-draining soil and making sure to allow the soil to completely dry out before watering again will make your cactus happy.

IMPORTANT NOTE: If your moon cactus is not receiving enough light to use the amount of water you are providing, then it needs to be given more light. Cacti like A LOT of light.

They will thrive in west-facing or east-facing windows. They will be happy near a south-facing window as well. If they are placed more than a foot or so from a window, they will not receive enough light and watering them during light deficiency will cause issues.

I keep mine right on the window sill of a west-facing window to ensure it receives enough light.

Why does watering when the cactus is in low light cause an issue? Click here to read about it.

The plant uses water and light to photosynthesize or make food. Without the proper amount of light, the plant can’t photosynthesize so the water sits there unused. Its roots, sitting in the unused water, develop root rot which then kills the plant.

Saving the Rootstock

The rootstock is only incapable of supporting itself because it is using all of its resources to support the scion. If you remove the scion or ball cactus on top, then the rootstock will callous over and begin to be able to support itself.

Eventually, it will produce new growth, which it was not able to do previously!

Here’s how you can grow your own cactus using just the rootstock:

  1. Get a sharp, clean knife
  2. Use the knife to make a clean cut through the Hylocereus undatus cactus, below where the scion is. You want to remove all of the scion. It is okay to remove some of the Hylocereus undatus or rootstock as well.
  3. After the scion has been removed, place your happy Hylocereus undatus back in a sunny window where it will take some time to callous over.
  4. Make sure to water it only when the soil is dry and just give it time!

*This method assumes that the rootstock is still healthy (green and firm)

Here’s what happened when I did this to my own moon cactus!

I happily cared for my moon cactus for about 2 years before I noticed that it began to decline. It was then that I learned that I could save my dragonfruit rootstock by removing the scion.

I removed the scion on August 11, 2019

My new dragon fruit cactus appeared as if nothing was happening for a month.

Then I went to water it in mid-September and take update photos for this post. Look at what I found below!!

That little green nub on the right-hand side of the large photo is new growth! I am excited to report that my dragonfruit is happy and growing!

As you can see in the lower photos, it has fully calloused over and was given a nice gravel upgrade as well. So chic!

I think the small spur on the left side of the cactus in the large photo might be new growth too. Time will tell!

One month after removing the scion, September 16, 2019

Two months after removing the scion, October 15, 2019

Look at that growth!! Not only has the branch of the cactus grown exponentially, but you can also see an aerial root that has formed. The aerial root shows that this type of cacti is a climber in nature and is ready to begin its ascent if we provide it something to clamber up! Wow!

Saving the Scion

If you want to save the scion, you can remove the scion and graft it onto a new rootstock.

To learn how to do this, I will provide a link to a youtube video here that will show visual instructions.

Below are written instructions. I cannot include photos as I didn’t try to save my scion (explanation for why at the end of this section)

To graft your scion onto a new rootstock, you will need to:

  1. Purchase a new Hylocereus undatus of the appropriate size to be your new rootstock
  2. Make a clean cut into the rootstock, removing the top of the cactus (usually 3 or 4 inches above the soil is left)
  3. Now take your scion and cut out all of the remaining rootstock so just the circular area and the flesh of the scion can be seen. No green should be left.
  4. Then cut the top of the rootstock so that it becomes more of a dull point, similar to the indented area on the scion.
  5. Finally, you want to place your scion on top of your rootstock so the circle in the flesh on each cactus is lined up. This area is called the vascular cambium and is how the rootstock is able to support the scion.
  6. A rubber band can be used to secure the scion onto the rootstock until the two have grown together. It can take about 8 weeks for the bond to become secure.
Here’s my quick drawing of the vascular cambium. I’m not a graphic designer. Can you tell? 🙂

Why I didn’t save my scion: I did not try to do this myself because my personal feeling is that the scion is not meant to survive in nature. I let the scion die naturally after removing it, rather than grafting it to a new cactus that would be overtaxed trying to support the scion just as my Hylocereus undatus was.

It took a few weeks for my scion to die. In the meantime, I gave it its own pot, as shown above. I was attached after caring for it for a couple of years and didn’t want to just throw it away. 🙂

However, it is possible to keep moving your scion to a new rootstock as the rootstock perishes.

*This method assumes that the scion is still healthy (not brown or mushy; still vibrant)

An Alternative Option to Saving the Scion – Buying a Chin Cactus

Chin cacti that survive in the wild are similar in stature to the brightly-colored balls that many are attracted to with the moon cactus.

Chin cacti can come in many different colors, including variegated versions that have the neon pinks, reds, and yellows. Though admittedly, these versions are much harder to come by!

Unlike the moon cacti’s scion, these variegated versions have chlorophyll so they can support themselves! There is no need for a rootstock.

You can see my chin cactus featured above, with its neat tri-color effect. Green fading to a deep blue-purple fading to a pinkish purple near the base. This little guy is only about an inch in diameter, but chin cacti can be found larger as well.

This is just one example of many in the Gymnocalycium genus. Take some time to check them out. They are quite beautiful!

Tools for Your Cacti

All products are linked to Amazon via Amazon Affiliate Services.

Cactus Soil

This soil is great for use as an affordable, organic, pre-made cactus soil. I have used this with many of my cacti for years and they seem to love it.

Click the picture to be redirected to Amazon.

A Moisture Meter

Moisture meters are awesome because they answer the question definitively about whether your plant needs to be watered. If the meter doesn’t read a 1 or 2, your plant doesn’t need to be watered! I love the simplicity and that I can trust this device!

Click the picture to be redirected to Amazon.

White Pebbles

Here is a link to the new white pebbles I have added to my cactus. I love them. They are so pretty and from the same brand (Exotic Pebbles) that my other pebbles and sands are.

Click the picture to be redirected to Amazon.

Resources used for this article:

Click to read last week’s post: What is the Cause and Controversy of Variegated Houseplants?

Want to learn more about houseplant care? Check out these posts:

Lighting: How to Choose the Perfect Houseplant for the Lighting in Your Home!
Bright Indirect Light: Houseplant Care: What is Bright Indirect Light?
Watering: How to Water Your Houseplants Correctly Every Time
Passive Hydro: How to Propagate Houseplants Using Passive Hydro
Potting Mix: What Potting Mix Will Help Your Houseplant Grow and Thrive
Choosing a Pot: Pick the Right Pot For Your Houseplant
Exposing My Mistakes! Sharing My Biggest Houseplant Mistakes So You Can Avoid Them!
Propagation: How to Propagate a Hoya Lisa Cutting in Water
Fertilizer 101: Answers to the Most Common Questions About Fertilizer

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