Cacti & Succulents

Grow, Plant, and Nurture Your Moon Cactus Plants

Posted on by JAMES

Discover how fascinating moon cactus plants can be with their stunning colorful tops. Gardening enthusiast Madison Moulton explores the cultivation and care of Gymnocalycium mihanovichii in detail.

For a captivating addition to your garden, the moon cactus is a must-have. Its vibrant hues ranging from pink to orange create an almost surreal appearance.

These unique cacti have an intriguing backstory and growth patterns that set them apart in the world of succulents and cacti. Their minimal sunlight requirements, influenced by their native environments, make them perfect for indoor settings.

Keep reading to explore the allure of moon cacti, understand what makes them extraordinary, and learn how to care for them.

Moon Cactus Overview

Plant Type Cactus
Family Cactaceae
Genus Gymnocalycium
Species Gymnocalycium mihanovichii
Native Area South America
Hardiness Zones 11–12 (USDA)
Exposure Bright indirect light, some direct sun
Height 12”
Watering Requirements Low
Pests and Diseases Spider mites, mealybug
Maintenance Low
Soil Type Cactus mix

All About Moon Cacti

Top view, close-up of growing Gymnocalycium mihanovichii in black pots in a nursery. Cacti are made up of two cacti. The lower part is an upright, elongated, dark green cactus Myrtillocactus geometrizans with 4 ribs. And the upper part is round, plump, thorny cacti in different bright colors, such as red-orange and bright yellow.
Moonlight cacti are native to South America and are known for their neon colorful spiked tops.

Moon cactus plants stand out in a succulent collection due to their vibrant, spiny tops that almost seem to glow. It’s amazing how real these cacti are, considering their vivid colors.

The Gymnocalycium mihanovichii hails from South America, specifically from regions near Paraguay and Argentina. Its original appearance is a far cry from its cultivated colorful variants.

Interestingly, these cacti are naturally green, but genetic mutations during cultivation have led to the array of stunning hues we see today. They bloom in shades like orange, bright red, yellow, and even pink.

This lack of chlorophyll in moon cacti triggers the pigments in their cells to shine, resulting in their vibrant colors. However, this mutation comes with a drawback – they cannot survive on their own and must be grafted onto a chlorophyll-containing succulent.

That’s why you’ll always find these colorful cacti attached to a green base, usually species like Hylocereus. The base plant takes care of most of the essential functions to sustain the colorful top.

Are They Hard to Grow?

Close-up of two moon cacti in black plastic flower pots outdoors against a blurred background. Cacti have rounded bright yellow and bright red tops covered with thorns. The tops grow on dark green, 4-ribbed Myrtillocactus geometrizans cacti.
These cacti are quite difficult to care for due to the lighting needs of two different species in one.

While cacti are generally hardy plants, moon cacti are a bit more sensitive and challenging to maintain due to the unique lighting requirements of two grafted species.

Unfortunately, these colorful cacti are not long-lived, typically surviving for about a year or slightly longer under ideal conditions.

Despite their care complexities and shorter lifespan, moon cacti are fantastic additions to any succulent collection. Their unmatched colors, especially when they bloom, are truly remarkable.

Additionally, these cacti thrive indoors, making them suitable for indoor gardening – a feat that can be tricky for many other succulents. Moreover, they make delightful gifts if you ever get the chance to propagate them.

Planting

Top view, a hand holds a colorful cactus gymnocalycium mihanovichii variegata in a black plastic pot with akadama soil on a blurred background. The cactus is rounded, plump, fleshy, has 8 convex ribs covered with thorns. The plant is dark green with hints of light pink, yellow and deep pink near the top. Top view, a hand holds a colorful cactus gymnocalycium mihanovichii variegata in a black plastic pot with akadama soil on a blurred background. The cactus is rounded, plump, fleshy, has 8 convex ribs covered with thorns. The plant is dark green with hints of light pink, yellow and deep pink near the top.
Moon cacti prefer to grow in confined spaces with good drainage.

Moon cacti thrive when snug in their containers, preferring minimal empty space around their roots, typically not requiring repotting for years. If considering a decorative container change, ensure it is compact to prevent potential rot and has ample drainage. Alternatively, use a larger container as a cover without repotting, but remember to remove the inner pot for watering. Avoid water accumulation at the base to prevent rot.

To enhance aesthetics, add a layer of matching-colored fine gravel atop the soil to accentuate plant details.

How to Grow

Caring for a moon cactus is straightforward as they require minimal attention for survival. Despite their low maintenance, their colorful mutation typically limits growth and longevity. If your plant struggles, it could be due to its natural short lifespan rather than care errors.

Light

Close-up of a potted orange moon cactus on a sunlit windowsill. The cactus has a bright orange, round, plump, juicy top covered with spines and small, rounded cubs. The cactus is in a beautiful brown clay flower pot. The base of the plant is an upright, dark green cactus, Myrtillocactus geometrizans.
The lower part of the moon cactus prefers a lot of light, while the upper part is more sensitive and needs indirect sunlight.

Managing sunlight for moon cacti can be tricky due to their distinct needs. The top segment is sun-sensitive, requiring indirect light, while the lower part needs direct light for photosynthesis. Locating these plants indoors is ideal to shield them from intense sunlight while providing sufficient light for survival. When grown outdoors, monitor for sunburn risks in warmer climates.

Position your cactus where it receives a few hours of direct sunlight along with indirect bright light to maintain a balance between the plant’s different light requirements.

Water

Top view, close-up of a row of colorful moon cacti in white square decorative pots. The tops of the cacti are rounded, bright red, pink and yellow, covered with thorns.
This cactus requires little water, especially at low temperatures.

Maintain your moon cactus by providing sparse watering, as excess moisture can lead to root and base rot. Watering frequency depends on the plant’s size, generally requiring watering every couple of weeks after complete soil dryness. Refrain from watering during winter months to prevent potential rot due to reduced water requirements. Ensure proper drainage by watering until excess runs through the pot’s holes to mimic natural rainfall patterns.

When utilizing a decorative pot cover, always remove it before watering to prevent moisture accumulation and potential fungal growth.

Soil

Close-up of a male hand holding a small cactus in front of him in a brown plastic pot. The moon cactus consists of a bright red rounded top covered with spines and an erect, oblong, fleshy, dark green cactus below. The man is wearing a dark blue shirt. Close-up of a male hand holding a small cactus in front of him in a brown plastic pot. The moon cactus consists of a bright red rounded top covered with spines and an erect, oblong, fleshy, dark green cactus below. The man is wearing a dark blue shirt.
Use potting mix for succulents and cacti as it contains the perfect ratio of ingredients for good drainage.

For the health of your moon cactus, soil with good drainage, is critical. The existing soil should suffice without the need for replacement unless you plan on repotting. The current sandy, gritty soil with ample air gaps between particles should be replicated when you decide to change the pot.

If repotting is on the horizon, opt for a premixed succulent and cacti potting mix for the ideal drainage properties. These mixes maintain the necessary ingredient balance to prevent root rot and enhance aeration. Making your mix is possible by blending premium potting soil with horticultural sand to mirror the arid conditions these plants thrive in.

Given their minimal nutrient requirements, moon cacti prefer slightly nutrient-deficient environments, so skip adding compost or fertilizers during planting. These slow-growing plants are content with lean soil.

Temperature and Humidity

A close-up of a vibrant Gymnocalycium mihanovichii in a dark green plastic pot against a blurred background of many potted growing moon cacti. The plant consists of two cacti. A small, round, bright yellow, spiny cactus grows on top of a thick green cactus Myrtillocactus geometrizans with 4 ribs. Many tiny, round, bright yellow pups grow on top of the moon cactus. A close-up of a vibrant Gymnocalycium mihanovichii in a dark green plastic pot against a blurred background of many potted growing moon cacti. The plant consists of two cacti. A small, round, bright yellow, spiny cactus grows on top of a thick green cactus Myrtillocactus geometrizans with 4 ribs. Many tiny, round, bright yellow pups grow on top of the moon cactus.
Moon cactus thrive in hot, bright environments and dislike sudden temperature changes and drafts.

In its natural environment, Gymnocalycium mihanovichii basks in consistently warm temperatures. Resisting cold weather or frost, these plants are better suited to warm, brightly lit indoor conditions. Avoid exposing them to chilly drafts or abrupt temperature shifts by situating them away from cold-prone areas, especially in winter.

While moon cacti prefer drier air, they can tolerate increased humidity levels without significant harm. However, monitor for potential diseases or fungal issues in higher humidity settings than they’re accustomed to.

These plants’ adaptability to lower humidity levels makes them suitable for rooms where traditional tropical houseplants struggle.

Fertilizing

Close-up of a flowering cactus Gymnocalycium mihanovichii on a blurred green background. The cactus is rounded, plump, bright deep purple in color, with convex ribs covered with thorns. Small rounded pink pups grow on the ribs. At the top of the cactus, a bright pink, funnel-shaped, silky bud grows before flowering. Close-up of a flowering cactus Gymnocalycium mihanovichii on a blurred green background. The cactus is rounded, plump, bright deep purple in color, with convex ribs covered with thorns. Small rounded pink pups grow on the ribs. At the top of the cactus, a bright pink, funnel-shaped, silky bud grows before flowering.
Promote blooming by applying succulent fertilizer in the spring.

Moon cactuses generally don’t need fertilizer due to their habitat’s poor soil quality. Save fertilization for when a soil change is necessary to replenish nutrients or enhance drainage. If you aim to encourage flowering, use a succulent-specific fertilizer sparingly each spring, ensuring you follow recommended doses to avoid root damage.

Additionally, ensure optimal light levels to support blooming for enhanced results from fertilization.

Propagation

Gymnocalycium mihanovichii propagation differs from typical succulents and cacti as these plants rely on grafting onto a succulent rootstock for survival. The process, though unique, can be straightforward with the right equipment and a suitable plant ready for the transformation.

Step 1: Identify a Pup

Close-up of the pink top of the Gymnocalycium mihanovichii. The cactus has a rounded hot pink top with small round pups ready to propagate. The plant is covered with small sharp thorns. The terracotta flower pot is filled with decorative stones.
Close-up of the pink top of the Gymnocalycium mihanovichii. The cactus has a rounded hot pink top with small round pups ready to propagate. The plant is covered with small sharp thorns.
Before starting the process, ensure you select a sufficiently large pup for trimming.

To begin, pinpoint a pup that is large enough for propagation. These small spheres emerge from the cactus’ base under ideal growing conditions. Hence, adhering to a proper care routine is essential if you aim to propagate.

Ensure the pups chosen for removal are of decent size to allow trimming without compromising their rounded shape excessively.

Step 2: Twist it Off

Close-up of a pink-topped cactus plant against a blurred background of female hands. The plant has globular, spiny, bright pink tops attached to a dark green cactus.
To remove the pup, twist it in the opposite direction from the mother plant.

Prepare to remove the pup and any others ready to grow independently. Simply twist in opposite directions to detach the pups.

No need for gloves as the spines are not overly sharp, but consider protection if you have sensitive skin.

Step 3: Cut the Rootstock and Pup

Moon cactus grafting. Close-up of a woman's hands making a horizontal cut at the base of a cactus pup for further propagation. The pup is a succulent round cactus of bright pink color, covered with thorns.
Create horizontal cuts at the base of the pup and the top of the rootstock.

While most cacti can be planted in their own pots for growth, moon cacti require a different approach. You’ll need to select a suitable rootstock for grafting both plants together.

In most nurseries, Hylocereus undatus or dragon fruit is commonly used as rootstock due to its ideal size, whereas some growers prefer Myrtillocactus geometrizans for its longer lifespan. Make horizontal cuts at the base of the pup and the top of the rootstock to expose the flesh using a clean, sharp blade to prevent disease spread and promote faster healing.

Step 4: Grafting

Close-up of female hands taping a baby to a rootstock indoors on a wooden table. A bright pink baby moon cactus is taped to a Myrtillocactus geometrizans plant. Lunar cactus rounded, plump, covered with thorns. Myrtillocactus geometrizans has a single, thick, dark green stem with five ribs with areoles.
Position the pup in the center of the rootstock and secure it with tape.

Grafting may seem complex, but when it comes to cacti, it is a simple process of joining and taping them together.

Place the pup in the center of the rootstock and tape it securely for stability. The two wounds will eventually merge as they heal, creating a grafting point.

Step 5: Remove the Tape

Close-up of the pink top of a moon cactus rooted on top of the dark green cactus Myrtillocactus geometrizans against a blurred background. The moon cactus is rounded, pale pink in color and covered with thorns.
Gently remove the tape once the rootstock wound is healed.

Once the wound on the rootstock has mended, carefully remove the tape to avoid hindering new growth. With the propagation process complete, care for your new moon cactus like the parent plant.

Repotting

Repotting is essential only in cases where soil replacement is necessary for enhanced drainage and nutrient enrichment.

With their slow growth and limited lifespan, Gymnocalycium mihanovichii usually do not require repotting. However, if you have one thriving for several years, refreshing the soil becomes crucial. Over time, soil quality degrades, and repotting can help enhance drainage and nutrient retention.

To begin, gently lift the plant from its current container, being cautious at the base. Depending on the root spikiness, consider wearing gloves. Remove old soil around the base, delicately loosen the roots, and assess for vitality.

For a small plant, reuse the same container or opt for a slightly larger one if more space is required. Fill with succulent and cacti potting mix, replant at the same depth, avoiding deep burial that can lead to base rot and plant demise.

Allow a couple of days for the roots to recuperate before watering to minimize transplant shock. Subsequently, resume standard care for your moon cactus.

Common Problems

Gymnocalycium mihanovichii faces challenges despite minimal requirements, including potential pests, diseases, and other concerns. Explore some prevalent issues below.

Root Rot

Frequent watering, inadequate drainage, or improper soil mix can lead to root rot in moon cacti.

Excess moisture sensitivity makes root rot a common issue. Overwatering, poor pot drainage, or unsuitable soil composition can trigger this problem.

Signs of root rot manifest as softening and yellowing at the base, potentially progressing to affect the Gymnocalycium mihanovichii, leading to detachment at the graft point.

Once rot begins, salvaging the plant is challenging. Prune and graft the top of the cactus to a healthy rootstock to revive the Gymnocalycium mihanovichii. Adjust watering frequency, potting, and soil to prevent recurrence.

Sunburn

Prolonged sunlight exposure can cause irregular brown spots on moon cacti.

Irregular brown spots indicate sunburn due to excessive direct sunlight exposure. These cacti are sensitive to intense sunlight and should be shielded during peak hours to prevent damage.

To halt further browning, relocate the plant away from direct sunlight. Avoid extreme shade as compensating for light shortage can induce additional stress.

Pests

Common indoor pests such as mealybugs and spider mites may target moon cacti.

Moon cacti, especially post-grafting, can attract typical indoor pests like mealybugs and spider mites. Utilize neem oil for spot treatment and suffocation after washing off the bugs.

Frequently Asked Questions

Can moon cactus grow indoors?

To thrive, Moon cacti need protection from direct sun to emulate their native habitat conditions and prevent flesh scorching. Therefore, when placed in an area with bright indirect light and some morning sun exposure, these plants can grow happily indoors.

What is the lifespan of a Moon cactus?

These cacti have a relatively short lifespan due to slow growth caused by the lack of chlorophyll. While most Moon cacti live around a year, with the right care, they can survive for a much longer period.

Are Moon cacti naturally colorful or dyed?

Moon cacti are considered natural as the plants are real, but they do not occur in the wild as they are sold in stores. These unique mutations of the original species are grafted onto robust rootstock to sustain growth, creating the hybrid green cactus with vibrant tops that we are familiar with.

Do Moon cacti produce flowers?

When provided with the right conditions, Gymnocalycium mihanovichii may develop delicate blooms that complement its stunning colors perfectly. To encourage flowering, ensure they receive sufficient sunlight and fertilize once a year in spring.

Can Moon cacti thrive without grafting?

Due to their lack of chlorophyll, colorful Gymnocalycium mihanovichii plants cannot survive independently. They need to be attached to a cactus species containing chlorophyll to thrive and grow.

Final Thoughts

Moon cacti are truly captivating additions to any succulent collection, even if their presence is brief. They can serve as intriguing conversation starters in your indoor garden, adding vibrant hues. You might even have the opportunity to propagate new plants, honing your grafting skills and enhancing your collection simultaneously.

JAMES
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JAMES

James is an environmental gardener and passionate writer who holds a master's degree in agriculture. He graduated from Harvard University with a degree in environmental horticulture and has a particular interest in soil composition. Currently, James works as a researcher in plant research, where he continues to explore and advance knowledge in his field. His combined expertise in environmental gardening and soil science helps him contribute valuable insights to both academic and practical gardening communities.

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