Imagine a cactus that glows like a neon sign in the desert night. Enter the moon cactus: a vibrant mutant that defies nature’s rules.
This grafted wonder, scientifically known as Gymnocalycium mihanovichii, adds a splash of color to any succulent collection.
While it may demand more attention than its hardier cousins, the moon cactus offers a unique blend of beauty and botanical intrigue.
Ready to cultivate your own miniature marvel? Let’s explore the world of these captivating, colorful cacti.
Quick Guide to Moon Cactus
Here’s a table with data for the Moon Cactus:
Characteristic | Details |
---|---|
Scientific Name | Gymnocalycium mihanovichii |
Genus | Gymnocalycium |
Family | Cactaceae |
Order | Caryophyllales |
Also Known As | Hibotan cactus, Ruby ball cactus, Star flowered cactus, Red cap |
Mature Size | 2-6 inches in diameter |
Sun Exposure | Bright indirect light to partial shade |
Soil Type | Well-draining, gritty soil |
Soil pH | 6.0 – 7.5 |
Bloom Time | Rarely blooms |
Flower Color | Large and colorful when it does bloom |
Hardiness Zones | 11-12 |
Native Area | South America |
Sun Requirements
Because the moon cactus is essentially two cacti grafted together, finding the perfect lighting can be a bit tricky.
The host cactus, often a Hylocereus (dragon fruit), loves ample sunlight. However, the colorful Gymnocalycium mihanovichii perched on top cannot tolerate direct sunlight.
The solution? Place your moon cactus in bright but indirect light. A spot near a south-facing window (but not directly in it) or an outdoor area with dappled sunlight works well.
You might need to experiment a bit to find the ideal location where your moon cactus thrives.
Hardiness
While moon cacti are drought-tolerant, they’re not fans of the cold. Keep them away from temperatures below 40°F (4°C). They aren’t suitable for planting in the ground outside of Zones 11-12.
If chilly nights are on the horizon, protect your moon cactus with a blanket or, better yet, bring it indoors. During the warmer months, they can happily live outside in a pot, ready to be relocated indoors when winter arrives.
Toxicity
Moon cacti are generally non-toxic, making them safe around pets and children. However, their spines can pose a prickly problem, so it’s wise to place them out of reach.
Additionally, since the host plant can vary, it’s best to err on the side of caution regarding potential toxicity.
Primary Growth Season
These cacti are slow growers, but you’ll notice most of their development from late spring through early fall.
Typical Size
The colorful top of the moon cactus usually grows just an inch or two high. The overall height of the plant depends on the rootstock but typically ranges from 4 to 12 inches tall.
Flowers
Some might mistake the vibrant ball atop the moon cactus for a flower, but these cacti can produce their own blooms.
When conditions are ideal—usually in late spring or early summer—they may surprise you with pink, red, or even white flowers that emerge directly from the colorful top. However, flowering is rare when they’re grown indoors.
Growing the Moon Cactus
Understanding the origin of your moon cactus is key to meeting its needs. Despite its adorable appearance, the moon cactus is a bit of a botanical curiosity—a mutant, if you will.
In their native South American deserts, Gymnocalycium mihanovichii cacti are green due to chlorophyll, which masks their other pigments. The cultivars sold as houseplants are mutations that lack chlorophyll, revealing their vivid underlying colors. Without chlorophyll, these beauties can’t photosynthesize and thus can’t survive on their own. To live, they’re grafted onto a host cactus, typically a Hylocereus, which provides the nutrients they need.
Caring for a moon cactus means tending to both the top and the host. It’s important to note that even with the best care, moon cacti often have a lifespan of just a few years. Over time, the host cactus may weaken from supporting both plants. When it dies, the moon cactus will too—unless you regraft it onto a new rootstock.
Where to Plant
Due to their sensitivity to cold, moon cacti should only be grown outdoors year-round in Zones 11-12. Even in these zones, it’s wise to cover them or bring them indoors if temperatures dip below 40°F (4°C).
Indoors, place your moon cactus in a brightly lit area that avoids direct sunlight. A shaded sunporch or a location near a bright window works well.
Container
Moon cacti, like all succulents, require excellent drainage. Choose a pot with a large drainage hole. An unglazed clay pot is ideal because it helps absorb excess moisture.
Avoid overpotting—select a container that’s proportionate to the size of your cactus. Too much soil can retain excess moisture, leading to root rot.
Soil
Use a well-draining cactus or succulent mix. If you prefer to mix your own soil, combine regular potting soil with coarse sand, perlite, or pumice to enhance drainage.
Maintenance and Repotting
Moon cacti remain small and don’t mind crowded roots, so repotting isn’t frequently necessary.
Typically, repotting every few years to refresh the soil is sufficient. Signs that it’s time to repot include roots growing out of the drainage holes or the soil becoming depleted of nutrients.
If you decide to repot, do so in the spring at the start of the growing season. Water the cactus a few days before to hydrate the roots, making them more resilient during the transition.
While moon cacti don’t require pruning, you can remove any offsets (“pups”) that appear if you prefer to maintain its shape. Using a sharp, sterile blade, carefully remove the pups. These can be grafted onto new rootstock to propagate new moon cacti.
Watering
Overwatering is the most common mistake with moon cacti. These plants are drought-tolerant and prefer their soil to be on the dry side. Overwatering can lead to root rot and attract pests.
Water your moon cactus using the “soak and dry” method:
- Check for Dryness: Ensure the soil is completely dry at least an inch below the surface.
- Water Thoroughly: Place the pot in a sink and water until it runs out of the drainage hole.
- Drain Completely: Allow excess water to drain away and avoid letting the pot sit in water.
- Wait to Water Again: Let the soil dry out completely before the next watering.
During the growing season (April to September), water when the soil is dry. In the winter, reduce watering significantly, as the cactus is dormant and requires less moisture. Be sure to avoid overwatering at any time of the year, as this can lead to root rot and other issues. Additionally, ensure the pot has proper drainage to prevent water from pooling at the bottom. For more tips on how to care for fishbone cactus, place it in bright, indirect light and provide a well-draining soil mix suited for cacti and succulents.
Fertilizing
Moon cacti have modest feeding needs. If planted in fresh soil, they may not need fertilizer at all.
If you choose to fertilize, use a diluted (half-strength) liquid cactus fertilizer. Apply it sparingly—no more than once every two months during the growing season.
- Instantly feeds succulent plants, including cacti
- For all cacti, jade, aloe and other popular succulents
- Feeds instantly
- Able to apply directly to the soil or can mix with water
- Feed every 2 weeks
Pests and Diseases
The most common pests are mealybugs and scale insects. If you notice these pests, you can remove them manually or dab them with a cotton swab dipped in isopropyl alcohol. For more severe infestations, spraying with alcohol can help.
Root rot is another concern, usually caused by overwatering. Ensure your cactus has proper drainage and avoid watering too frequently.
Propagation
Since the colorful top of the moon cactus can’t survive on its own, traditional propagation methods won’t work. However, you can create new moon cacti by grafting offsets from the mother plant onto new rootstock.
How to Graft a Moon Cactus
Materials Needed:
- A healthy offset (pup) from a moon cactus
- A suitable host cactus (like Hylocereus)
- A sharp, sterile knife or razor blade
- Rubber bands, string, or tape
Steps:
- Prepare the Plants:
- Water your moon cactus three days before grafting to hydrate it.
- Sterilize Your Tools:
- Use alcohol or hydrogen peroxide to sterilize your knife or razor blade.
- Cut the Host Cactus:
- Slice off the top of the host cactus to create a flat surface.
- Bevel the edges
- by trimming them at a downward angle to reduce moisture and prevent the scion from shifting.
- Prepare the Scion:
- Remove a healthy pup from your moon cactus.
- Slice off a thin layer from the bottom to expose fresh tissue.
- Join the Cacti:
- Place the cut surface of the moon cactus pup onto the cut surface of the host cactus, aligning their vascular rings as closely as possible.
- Secure them together with rubber bands or string to ensure good contact.
- Wait for the Graft to Heal:
- Keep the grafted cactus in a location with indirect light and avoid watering for a week.
- After several weeks, the two cacti should fuse, and you can remove the support.