How to Grow and Care for Moon Cactus (Gymnocalycium mihanovichii)

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If you’re a plant enthusiast looking to add a touch of vibrant color to your succulent collection, then look no further than the Moon Cactus (Gymnocalycium mihanovichii). Known for its striking appearance and low-maintenance nature, these Cacti are a popular choice among both beginner and seasoned gardeners.

In this comprehensive care guide, we will explain everything you need to know, from basic information about moon cactus; to the ideal growing conditions like light, soil, water requirements, and more.

Gymnocalycium mihanovichii is a species of cactus native to desert habitats in various parts of South America. Named after the Croatian shipping businessman, Nicolás Mihanovic, it is known for its vibrant and colorful tops, which come in shades of orange, pink, red, and yellow.

However, the wild or original Gymnocalycium mihanovichii is a green cactus that lacks the vibrant colors seen in the grafted moon cactus. Its mainly characteristic a grayish-green body, with white and red reflections.

It is a dwarf cactus, growing up to only about 1.5 inches in height with a diameter of 1 inche. It has a solitary and spherical stem that is grayish-green or green with reddish tones and 8 to 10 obtuse ribs with a projection above the areola. The areoles are backward-facing and produce white wool.

This cactus is covered in spines, which are highly ornamental, with hairs or bristles emerging from small protuberances on the surface, the areolas.

Grafted moon cactus

The grafted Moon Cactus on the other hand is made up of two different cacti. The colorful tops that you see are the result of a mutation that causes a lack of chlorophyll in the plant, allowing other pigments within the cells to stand out. As a result, the top part cannot survive on its own and therefore needs to be grafted onto another succulent that contains chlorophyll

While they function as the same plant, they’re actually two separate cacti that have a parasitic relationship. This ensures that species that are not conducive to life in our environment are able to fully adapt, including cacti in our homes with a striking and unique appearance.

The most common base used for grafting moon cactus is a species from the Hylocereus genus, although other plants can also be used. The base plant provides the necessary nutrients (through photosynthesis) and support for the colorful top to thrive. Because of its ability to produce chlorophyll, the base cactus needs a lot of sunlight whereas the top doesn’t.

Ninety-eight percent of all of these colored novelty grafts are produced in Korea; they have the whole technique down to a fine science, and they produce millions of them. This grafting process creates a visually striking plant with a green base and a vibrant top.

Moon Cactus Flowering and Bloom Time

Moon cacti produce beautiful bell-shaped or funnel-shaped flowers, measuring approximately 1.5 to 2 inches in length. These flowers do not open fully and are usually orange, pink, red, or yellow, depending on the color of the top.

The exact bloom time can vary, but they typically flower in late spring or early summer and tends to happen more when they’re outside. The blooms are relatively short-lived, lasting only a few days to a week. The fruit of the plant is spindle-shaped or fusiform (ellipsoidal in shape), containing numerous black/brownish seeds.

Regardless of indoor or outdoor growth, they thrive in bright shade and should avoid direct sunlight, making them suitable for indoor settings. Placing them by the brightest window is often enough without needing a grow light.

Moon cactus care

Here are some basic tips on how to care for your succulent Gymnocalycium mihanovichii. These recommended care instructions apply to both the grafted moon cactus and the original.

Light

Gymnocalycium mihanovichii requires bright indirect light, most of the year, (except during the winter cycle) for the base plant to photosynthesize and thrive. However, direct sun can damage the colorful upper part and cause the colors to wash out, so it is recommended to keep them in the shade with little exposure.

For your plant’s health, place it in a spot with a few hours of direct sunlight and the rest of the day in bright but indirect sunlight

Water

When it comes to irrigation, Moon cacti prefer less water rather than more, as the roots and base of the plant are sensitive to rotting in constantly moist soil. Water your moon cactus thoroughly, allowing the soil to dry out completely between waterings.

You can inset your finger into the siol to feel the moisture. If it feels dry, then you can water it. During the summer months, the plants might need frequent watering, especially if it has been moved outside. Plants in small pots will only need weekly watering.

During the winter months, it is best to avoid watering altogether as the plant requires very little water during this period, with watering to resume in the early spring

If rot sets in, saving the plant becomes challenging, so erring on the side of too little water is advised to reduce excessive growth and avoid rotting.

Temperature and Humidity

This cactus enjoys temperatures ranging from 70-100°F (21-37°C) but demands cooler temperatures during the winter months. Starting in the late fall, this cactus should be kept between 50-65°F (10-18°C), and away from central heating vents.

The cooler spell is demanded over the course of the entire winter, during which time the segments of the cactus will turn a light gray color. Failure to provide these controlled winter conditions will result in plant death the following spring.

If grown outdoors, they are not cold-hardy. Bringing them inside during freezing weather is recommended, and covering them with frost cloth for a few days might be sufficient.

Like most cacti, this plant generally prefers drier air, but they can tolerate higher humidity levels as well.

Soil

Moon cacti prefer well-draining soil with a low pH to prevent root rot. A potting mix specifically formulated for succulents and cacti (for example, a mix of 1:1 Cactus soil and perlite) is ideal, as it provides the perfect ratio of ingredients for good drainage. Make sure the soil meets the needs of the host cactus on the bottom.

If planting in a container, please ensure that the container has drainage holes to allow excess water to escape. When repotting, make sure to replicate the sandy and gritty texture of the existing soil. Avoid mixing in compost or fertilizers, as moon cacti do not require high nutrient levels

Fertilizer

Fertilizing moon cactus is an important aspect of its care to ensure vibrant colors and robust health. These plants rely on their green rootstock for survival, so proper fertilization is crucial. Nitrogen, phosphorus, and potassium are the essential nutrients that support the growth and overall health of the cactus.

Fertilize moon cactus once a month during the growing seasons of spring, summer, and fall with a liquid fertilizer. It is recommended to choose a balanced NPK ratio, such as 1-1-1 or 2-1-1, with a bit more potassium for cacti.

Avoid over-fertilization, as it can lead to leaf burn, wilting, stunted growth, and salt buildup. Remember to dilute liquid fertilizers, water the cactus before fertilizing, and apply fertilizer during the active growing season.

Moon cactus lifespan and Propagation

These plants rarely last more than a few years since the upper scion and the lower rootstock grow at different rates, which eventually destroys the graft union between the two sections. In this case, you will have to to separate the crown and graft it onto a new rootstock cactus.

To do this, cut a green stem about approximately 4 inches long and let it heal. When it has rooted, you have to make an incision at the top and place a sapling taken from the upper globe of another cactus.

You may choose to graft it onto the same plant, split the base, or use a new rootstock to graft the baby on top. The best season for planting is spring or summer when faster growth is favored.

However, the process of grafting moon cactus is not simple, which is why it is most convenient to buy it already with the process completed

Repotting and Transplanting Moon Cactus

These plants are slow-growing, but they should be repotted every three to four years to rejuvenate the plant with fresh soil. Repotting should preferably be done during the warm growing season.

To repot a cactus, make sure the soil is dry before repotting, and then gently remove the pot. Place the plant in its new pot and fill with cactus mix potting soil, spreading the roots out as you repot. Leave the plant dry for a week or so to reduce the risk of root rot, and then begin to water lightly.

Grafting Moon Cactus

This is a fairly involved undertaking that requires some skill and knowledge of grafting techniques; It is not actually difficult but very precise. The process involves carefully joining the cut surfaces of the rootstock and scion, allowing them to heal and grow together.

The cactus that is usually used for the bottom part is a Hylocereus or a similar type of jungle cactus. The top of one of these is cut off, and another type of cactus is also cut and placed on top.

This is the tricky part: you need to know a bit about each plant’s vascular system – the part that gets the food and water around in the plants. It’s not unlike trying to re-attach a severed limb.

You have to be sure that the veins and nerves all line up to heal together. Typically the two cactus should be somewhat of the same diameter to help in the process.

Pests and diseases

Moon Cacti are generally resilient to pests and diseases but can occasionally fall prey to common cactus pests such as mealybugs and spider mites. Make sure to inspect your plants regularly for any signs of infestation, such as webbing, discoloration, or wilting.

If detected, promptly treat the affected cactus with an appropriate insecticide or horticultural soap. Additionally, practicing good hygiene,such as removing any fallen debris or dead leaves, can help prevent pest and disease problems.

Moon Cactus Problems

While the moon cactus is a tough, easy-to-grow plant , there are a few potential problems to be aware of:

  1. The color fades: If the colorful red, yellow, or orange top portion fades, it’s usually because the moon cactus is getting too much direct sunlight, which is causing the pigmentation to wash out. Move the plant to a location that gets bright and indirect light.
  2. The plant begins to collapse or die: Overwatering can cause root rot to set in, gradually causing the lower host cactus to collapse. If the upper part is detaching because the two cactus pieces grow at different rates, it’s not uncommon for the graft to separate after a few years. At this point, the best strategy is to separate the top portion and graft it onto another rootstock cactus.
  3. Edges of the colorful cyan turn brown: When the top portion begins to turn brown around the edges, there are two possible causes. The plant is getting too much water, or it’s getting too much sun.

FAQs

Is Moon Cactus toxic?

Moon cacti, scientifically known as Gymnocalycium mihanovichii, are not considered toxic to humans and pets. However, they have sharp spines and glochids that can stick into fingers, so keep them away from children and pets.

Can moon cactus grow without grafting?

No, grafted moon cacti cannot grow without grafting. They are typically mutants that lack chlorophyll, which is necessary for photosynthesis. As a result, they must be grafted onto a rootstock cactus to survive

How big can Moon cacti get?

They can grow to about a foot tall, depending on the aggressiveness of the rootstock, and the top may get a bit larger. Despite variations, they fare well in smaller containers.

How often should I water my Moon Cactus?

Water your Moon Cactus thoroughly when the soil is completely dry. During the active growing season, this may be once every 1-2 weeks. In the dormant season, reduce watering to once every 3-4 weeks.

Growing indoors may not induce true dormancy, so keeping an eye on them is crucial. Always lean toward too little water rather than too much.

Can I place my Moon Cactus outdoors?

Moon Cacti can be placed outdoors, but it’s important to protect them from direct sunlight and extreme temperatures. Choose a shaded or partially shaded area and bring them indoors during cold winter months.

Can I grow Moon Cacti in terrariums or enclosed containers?

It’s not recommended to grow Moon Cacti in enclosed containers as they require good airflow and can be prone to rot in humid environments.

How do I know if my Moon Cactus needs to be repotted?

If your Moon Cactus has outgrown its current container or the soil is no longer draining properly, it’s time to repot. Additionally, if you notice declining health or stunted growth, repotting may be necessary.

Can I propagate Moon Cacti through other methods besides grafting?

While grafting is the most common method of propagation for Moon Cacti, you can also try propagating them from offsets or pups that may form at the base of the plant.

Disclaimer: The information provided in this article is for educational purposes only and does not replace professional advice. Always consult with a horticulturist or gardening expert for personalized guidance.

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