Why is Your Moon Cactus Dying and Can It Be Saved?

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

How to save a moon cactus

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 (the green stalk supporting the colorful cactus on top)
Saving the Scion (the colorful, spiny top cactus)
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 hurts 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)

What is a moon cactus and why aren’t they meant to live long?

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.

Here’s what happened when I saved 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 Moon Cactus – 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!

Resources used for this article:

Submit your plant questions below to have them answered in a future post!

14 Comments

  1. Jo-Anne

    I seem to have lost the Scion and I do not know why. I will check the roots for the cactus at first.

    Reply
    • Colleen

      I hope you were able to find the issue. Let me know if I can help!

      Reply
      • Kenna

        I followed these directions to save the rootstock 5 months ago and I just noticed a tiny arm starting to grow off my cactus! I was wondering how your cactus looks now since your last update was over a year ago. Did you give it support to climb on?

        Reply
        • Colleen

          That’s so exciting that your little cactus is growing a new arm!! I’m so happy to hear that the steps worked for you as well. 🙂 My cactus has grown many vining segments that definitely needed support. I ended up adding bamboo skewers meant for shish kabobs with string surrounding them to create a trellis for the arms to climb. I’ll try to take a picture soon and update the post. I hope your cactus continues to thrive!

          Reply
  2. Penney

    With havin so much content do you ever run into any issues of plagorism or copyright violation? My site
    has a lot of unique content I’ve either created myself or outsourced but it looks like a lot
    of it is popping it up all over the web without my authorization. Do you know any methods to help stop content from being ripped off?
    I’d genuinely appreciate it.

    Reply
    • Colleen

      Hi Penney, I haven’t been concerned so far with plagiarism, but I do understand it can be a big concern. If you are using wordpress for your site, there are a good number of plugins that allow you to better control your content. Some of them restrict people from printing the content, others control whether or not you can copy content on a site, and still others will watermark images and things. I hope this helps! Good luck with your site 🙂

      Reply
  3. Lake

    I believe this is what I have, it was given to me by a friend. The top section of the cactus is papery and white but the bottom seems to be fine, it’s grown a new branch and an areal root in the past couple of months. I’m unsure whether or not to prune the dead section as the rest of the plant seems healthy.

    Reply
    • Colleen

      I agree, it sounds like you might have a moon cactus. You can prune the top off safely without compromising the health of the bottom plant. If you cut off the top and there is any of the top’s flesh still there or any discoloration in the live cactus, cut a little farther down to fully remove the flesh of the top cactus and any infection. After that it will just need a few days to heal and callous over!

      Reply
  4. Naomi G Klapstein

    I’m wanting to save my stock like this but I’m curious about the gravel as mine has been in soil. Are your growing it in just gravel or is there soil in there? I’d like to use the same method I prefer the look of yours and I have the same white rocks.

    Reply
    • Colleen

      Hi Naomi, great question! I have the cactus planted in a 50/50 mix of perlite and houseplant potting mix. The rocks are used as a top dressing both because I like the look of it and because it discourages fungus gnats from moving in! 🙂 Good luck with your little cactus!

      Reply
  5. Ashley

    Hey, my moon cactus is dying. The scion is starting to shrink and the root stock has. Evoke lighter in color as well as very thin. It does not feel mushy, but also doesn’t feel like it has meat inside , is this still salvageable?

    Reply
    • Colleen

      Hi Ashley, I’m so sorry I didn’t see this comment sooner. If you would still like help, email me a few photos and I might be able to help more. My email is colleen AT anaturalcuriosity DOT org. Have you checked the condition of the roots yet? If so, how were they doing?

      Reply
  6. Melissa

    Hi, I have a ruby moon cactus and I notice the scion seems to be dying, parts of it are going yellow/brown and falling off, the rest of the plant looks healthy enough to me! Any suggestions?

    Reply
    • Colleen

      Hi Melissa, I’m so sorry I didn’t see this comment sooner. I would love to help. Send me some pics of your cactus via email to colleen AT anaturalcuriosity.org

      Reply

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