How to Care for and Grow the Moon Cactus

The moon cactus is a cacti that you can find growing in South America’s deserts in Paraguay, Argentina, and Brazil. It’s a member of the Cactaceae family, and it’s a succulent plant that is also called the star flowered cactus, ruby ball cactus, and the red cap. When the moon cactus reaches maturity, it will only get up to two inches wide and offer clusters of sharp, small spines.

As a houseplant, the moon cactus is a mutant that doesn’t produce chlorophyll, and this is why it has such brilliant colors that range from neon yellow to hot pink. Since there is a lack of chlorophyll, you have to graft it to a rootstock cactus to make it survive. It’s common to graft the moon cactus to the dragon fruit (Hylocereus undatus), but you can combine it with a green cactus from any species.

The moon cactus is a pretty, small houseplant that needs minimal care to survive and thrive.

Moon Cactus Origins

This small cactus plant with the vivid colors is available in the shops or markets, but they’re not as striking as wild cactus plants. They come with bright red, pink, yellow, or orange coloring on them. However, since this cactus has neon colors, it can’t produce the chlorophyll that is necessary for the plant to live. To save this plant, you’ll transform this round grafted cactus into a regular grafted cactus. You can use any color to create a moon cactus.

Generally speaking, the species used for grafting you can get in any garden center. You’ll see a star shape on the stems, and this lends to the name of the star-flowered cactus. It’ll survive as long as you take care of it, but it’s quick to die with neglect.

Moon Cactus – Quick Overview

Bloom Time:	Varies but usually in the summer
Botanical Name:	Gymnocalycium mihanovichii
Common Name:	Ruby ball cactus, moon cactus, and ruby red cactus
Flower Color:	Neon from hot pink to yellow
Hardiness Zone:	11 and 12
Mature Size:	Varies depending on the rootstock
Native Area:	South American Deserts
Plant Type:	Herbaceous perennial
Soil pH:	Acidic to neutral at 5.5 to 7.0
Soil Type:	Fast-draining and rich cactus mix
Sun Exposure:	Shade or partial sun

How to Grow and Care For Moon Cactus

The bright ball of flowers that sit on the very top of this cactus is a charming draw for a lot of people, especially when you look at the plant’s compact growth habit.

It’s very hard to mistake the moon cactus because they come with the bright yellow, pink, or orange coloring. The bright neon colors usually come in the shape of a rounded ball with thorns, and they sit on top of another green cactus. This little plant is a funny one because it’s two plants in one, and it’s the product of a human design.

Growing and taking care of the moon cactus isn’t a hugely difficult task at all. They’re very low maintenance plants, and you can care for several of them at once without a problem. They can add life or color to your windowsill or porch, and they’re excellent for beginners due to thow undemanding they are.

Fertilizer

Providing healthy food to your moon cactus is one of the most essential tips we’ll offer here. However, you don’t need to feed this plant very often to keep it happy. It’s a very good idea to use a fertilizer with a good nutrient mix and minerals that can help strengthen your cacti. Monthly fertilizer applications can keep them healthy, and avoid using inorganic fertilizers to feed your plant. It’s best to use organic fertilizers to feed your moon cactus. Read the instructions on the packet and mix it according to these directions.

You should also practice flushing the soil once a month before you feed it. You’ll do this by thoroughly watering the plant. Use roughly four times the pot’s volume in water to flush it, and allow the water to drain completely before you add your fertilizer. Always get in a routine and follow it when you feed them to avoid giving them too much. Overfeeding can damage the plant.

Humidity

Humidity encourages healthy cactus growth. When it comes to humidity needs, this cacti isn’t as picky as others. Moisture will help to keep the soil damp, and this is essential for any cactus plants. You’ll want to set up relatively humid conditions for this plant’s growth. However, it can grow in low humidity. To pull this off, you’ll want to make sure your soil is dry before you add any moisture. If the soil gets too moist or it’s already damp, it’s too much water. Mist the plant to keep it healthy and to provide moisture without soaking the soil.

Soil

Ideally, you’ll get a sandy, aerated soil mix that lets the water drain well. Adding small stones or pebbles to the mix can also help create a gritty cactus soil. They prefer soil that is neutral to acidic, just like most cacti. A fast-draining but rich mix with a lower pH is the best way to go. The soil also has to match the needs of the host cactus on the bottom of the plant.

A very gritty and well-draining soil is essential for the moon cactus to stay healthy and thriving.

Sunlight

This plant requires a lot of indirect, bright sunlight. The grafted cactus on the top is tolerant to shade and it won’t tolerate direct sunlight well. The green cactus that acts like a stem needs more direct light. So, to grow a healthy moon cactus, you’ll have to adjust until you find the right light balance. To achieve this, the best location is in a bright spot in your home.

Put your moon cactus in a west or east-facing windowsill to give it a lot of bright sunlight but limited direct light. If you put it in a south-facing window, you want to place it back from the window to prevent scorching or burning. If parts of the cactus start to turn white or bleach and develop scars, you want to move it back from the sun. A plant that turns yellow is also an indication that it has too much light.

Temperature

This plant prefers slightly warmer temperatures, and the average room temperature is usually ideal. Put this plant by a window to give it the heat it needs to grow well while shading it from the sun. They grow best when the temperature stays between 64°F and 77°F or 18°C to 25°C.

This gets a bit more complicated because the bottom cactus usually has slightly different temperature requirements than the moon cactus itself. However, the base is slightly hardier, so it’ll survive temperatures that dip a bit below the 64°F (18°C) range without any damage. Make a point to keep your moon cactus away from cold drafts inside and direct heat.

If you live in planting zones 10 or 11, you can grow your moon cactus outside. To do so, you’ll want to find a bright spot in the yard that has partial shade. For temperate climates, you could transfer the cacti outside in pots during the warmer summer months. When the temperatures start to drop in the autumn months, bring them back inside. They’ll die if the temperature falls below 48°F (9°C).

Water Requirements

You’ll have minimal water requirements for your moon cactus. This isn’t the type of plant you’ll keep on your normal houseplant watering schedule. If you live in a location that gets a lot of rainfall and you have this plant outside, it’ll do better under a covered porch. You can feel the soil to tell if your plant needs water. If you touch it and it’s dusty and dry, you can give it a very light drink. You don’t want to soak the soil.

Make a point to never overwater to the point that it’s waterlogged or soggy or the potting soil spills over the sides. Never give it so much water that it’s sitting in a soggy pool of dirt. You also want to cut off watering for established plants during the winter months, so this is after your plant is a year old. If you have a young moon cactus, a tiny amount of water during the winter months is more than enough.

This plant calls for shallow, unglazed pots with excellent drainage capabilities. The containers or pots should have adequate drainage holes so that the water can run through and out. You should also put a very thin gravel layer in the bottom of the pot before you add the plant to help with drainage.

Propagating Moon Cacti

The moon cactus isn’t appropriate for propagation, but you can graft your own moon cactus at home. Many cacti species graft very easily, and the process is relatively simple for any gardener to try, no matter if you’re experienced or a beginner. Don’t be intimidated by the plant’s thorns either. To graft it, you’ll cut the scion from the old rootstock and the upper portion of the seedling cactus using a sterilized and sharp knife. You’ll see dark vascular tissue on the scion and the host cactus. Bring your scion closer and try to align the vascular tissue.

Once you align them, you want to wrap the scion cactus and the bottom of the container that the host is growing in vertically using rubber bands. Wait for the tissues to fuse before you remove the rubber bands. If you’re lucky enough to get a moon cactus that produces offsets, you can propagate the plant once it matures. Some scions can produce clusters of offsets that you can separate easily from the mother plant. Remove the offset carefully and let it dry for a day or two before planting it in well-draining potting soil. It will eventually need a host cactus to survive.

Even though you can’t propagate a moon cactus like you can a traditional succulent or other type of houseplant, you can graft it.

Potting and Repotting the Moon Cactus

This is a slow growing plant, but you want to repot them every three or four years to add fresh soil to the pot. Repotting should take place during a warm growing season. To repot it, you want to make sure that the soil is dry and gently remove the plant from the pot. Gently knock away the oil soil from around the roots, and trim away any dead or rotted roots you see. Treat any cuts on the cactus with fungicide, and put the plant in the new pot before backfilling it with a gritty cactus potting mix. Spread the plant’s roots out as you repot it, and leave it to dry for a week or so to prevent root rot and then water it very lightly.

Pruning Moon Cacti

Considering the slow growth and small size, you won’t need to prune the moon cactus very much. However, if it happens to get overgrown, you can trim off any broken or excessive foliage. You usually will prune your cactus after it finishes flowering for the season. Take a sharp and clean pair of pruning shears and follow the plant’s leaves all of the way back to the main stem and cut at this point. Get rid of any plant tissue and leave the cactus to bloom again.

Overwintering Your Moon Cactus

If you have a potted moon cactus that you’re growing on the patio, you should bring it indoors when the weather starts to dip below 50°F or 10°C. The ideal winter temperatures range between 50°F and 60°F (10°C to 16°C). So, you want to give your plants a relatively cool indoor location for the winter and cut back on the feeding.

Getting the Moon Cactus to Bloom

The flowers on this plant can be relatively indistinct, so you usually won’t try to coax them to flower. In some cases, your plant can produce two different flower types since the lower rootstock and the grafted scion are two different cacti species that have their own flowering patterns. This isn’t a problem if the plant doesn’t have any flowers at all.

Common Pests, Plant Diseases, and Problems

Cacti are usually free of the most common pests that plague houseplants, but mealybugs and spider mites can be a problem. You can control them using a chemical pesticide or neem oil. The biggest disease is root rot, and poorly draining soil and overwatering cause it. If the base of your moon cactus gets mushy and soft, you want to stop waiting. You may have to regraft the upper scion to a new host plant and get rid of the old one. A few other problems include:

Beige Spots

This plant is very sensitive to too much light, and it’ll develop beige patches when it gets sunburned. If this happens to your moon cactus, you want to shift them to a space that has less sunlight to allow it to heal. Give them adequate water to help them recover from sunburn.

Color Fades

If the vivid orange, red, or yellow top portion starts to fade, this is usually because your plant is getting far too much direct sunlight. This causes the pigmentation to wash out. You can combat this by moving the plant to a location that gets indirect but bright light.

Collapse

Overwatering your cactus can allow root rot to take hold. Over time if you don’t treat it, this will cause the host plant’s columnar tower to collapse. This is due to the fact that the plant gets far too mushy to hold itself up.

Detaching Upper Ball

Since the two cacti species will grow at a different rate, it’s not uncommon for the graft to separate after a few years of growth. When this happens, the best thing you can do is separate the top portion from the rootstock and graft it to another plant to start the process over.

Edges Turning Brown

When your colorful part of the moon cactus starts to show a brown coloring around the edges, there are two possible causes. First, you could be giving your plant too much water, or you could have it in a place that gets too much sun. Cut back on the watering and move it to a more shaded area to fix it.

Root Rot

Too much water will kill the plant’s root system, and these plants are very prone to developing issues with root rot if you overwater them. If the lower portion of the rootstock starts to get soft, it’s very likely root rot is present. You can salvage the plant by cutting above the mushy portion and replanting it as a cutting. However, it has a very low survival rate.

Moon Cactus – Frequently Asked Questions

This plant looks very intimidating when you first see it, so it’s common to have a host of questions surrounding keeping it healthy and thriving.

The following are some of the most popular questions people have:

1. Are there other colorful types of cactus to consider?

The moon cactus isn’t the only colorful cacti you can get to grow as a houseplant. There are several other houseplants that are very colorful and have vivid flowers, including the Christmas Cactus (Schlumbergera spp.), Lady Finger Cactus (Mammillaria elongata), and the Ball Cactus (Parodia spp.). 

2. How long will your moon cactus live?

Unless you decide to regraft the upper portion of the plant onto a fresh rootstock cactus, this plant will die in a few short years. If you’re willing to try and regraft the plant, you can keep it growing for decades.

3. What does the moon cactus look like in the wild?

In native South America, this plant is a four inch, miniature plant that has a globular shape with 8 to 14 ribs. It’s a greenish-gray plant with burgundy accent colors. In the wild, you’ll find it growing in shaded locations under grasses or shrubs. The colorful versions you grow indoors are all cultivares people have selectively hybridized and bred since the 1940s.

Bottom Line

The moon cactus can be a gorgeous addition to your plant collection if you don’t have one yet. It’s relatively easy to keep happy and thriving, but due to the lack of chlorophyll and short life span, you should be ready to replace it in a few years. However, they’re a fun addition to your growing succulent collections, and this bright green plant can lend a pop of color to your home with minimal maintenance.