Gymnocalycium Mihanovichii “Moon Cactus”

Gymnocalycium mihanovichii

Last updated on August 1st, 2022 at 01:50 am

Gymnocalycium mihanovichii is a small member of the cactus family that occurs in the northwestern part of Argentina and adjacent areas of Chile. Like other species in the genus, Gymnocalycium mihanovichii grows in habitats that receive a temperate, maritime influence.

It differs from most of its relatives in several important ways: it is a relatively fast-growing plant that can produce flowers and fruits with little attention. However, while Gymnocalycium mihanovichiihas gained popularity for its tolerance of both cold and drought, it is a finicky cactus when it comes to handling.

If handled incorrectly from the beginning, Gymnocalycium mihanovichii can become difficult or impossible to grow indoors.

Gymnocalycium mihanovichii propagation

Gymnocalycium mihanovichii

Gymnocalycium mihanovichii is one of the few Gymnocalyciums that are easily propagated from both seed and cuttings. Cuttings will root faster than seeds in most cases, but only seeds can produce plants with identical characteristics to their parents.

Propagation via seeds is fairly easy, especially if you have more than one plant from which to collect seeds.

When the fruit is ripe, cut it in half lengthwise and remove the seeds. Then, clean off all the fleshy tissue. Place the seeds on a sterile surface (like a paper towel) and allow them to dry for 4-5 days or until they are hard and somewhat brittle. When you see the green embryo that looks like a tiny cactus, it’s time to plant the seeds.

Gymnocalycium mihanovichii is readily increased from cuttings, which are taken in spring or summer as growth begins. Cut off a stem and remove the lower leaves to expose a piece of the green tissue that will function as the “root.” Remove all but about 3-4 leaf segments from the cutting, and place it in slightly moistened coarse vermiculite (or a similar medium) in a small container. Cover it with plastic to keep the humidity high and place it in bright light, but out of direct sunlight.

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Growing Instructions

Sow the seeds on moist (not wet) vermiculite or other sterile media in small containers and cover them with plastic wrap to keep them from drying out. Keep them warm and in bright light. Germination should occur within 30 days, and you can then begin to harden them off for transplanting into individual pots.

Growth of seedlings transplanted from plugs to small pots or a large pot is often slow at first as the root system becomes established in its new container. Be patient with your plants, and don’t allow them to become too root-bound.

Pinching plants before they flower can encourage branching and further plant development.

In areas with warm winters, seedlings may not need protection over the winter months unless fall or spring frosts are likely; otherwise, summer protectors or a cold frame should be used to keep them from freezing.

The cutting will not root immediately, but within 7-10 days, roots should begin to form at the base of each leaf segment (where it was attached to the main stem). If it doesn’t root within 30 days, it may be necessary to transfer the cutting to a new growing medium that is different from what you originally used.

Seedlings should not be exposed to temperatures below 60°F (15°C) for any length of time, whereas mature plants will tolerate much colder temperatures. If your home is not heated, you can place the plants in a cold frame to protect them over winter or in spring and fall months when temperatures may dip below freezing.

Gymnocalycium mihanovichii care

Gymnocalycium mihanovichii


Gymnocalycium mihanovichii requires bright light but not direct sunlight. Some growers recommend full sun, and although some plants can withstand the low humidity and strong sun that accompanies such growing conditions, most cannot. They grow well under fluorescent lights in a greenhouse or indoors near windows where they can receive diffused sunlight from an eastern or western exposure.

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A minimum winter temperature of 15°C (59°F) is recommended, and plants should be kept at a slightly higher temperature during the day. [One method to achieve this is with passive solar lighting – windows positioned to face the sun.]   Potted plants are brought indoors from late fall through early spring for protection from frost.

Gymnocalycium mihanovichii is easily damaged by prolonged exposure to direct sunlight. The leaves turn brown and dry when the plant is moved from the shade into bright light, or when it suddenly gets too much light after being kept in darkness for a long time. Keep this species shaded for at least one month after transplanting to a brighter location.

If the air is very dry, it is advisable to mist plants regularly or place them on trays of damp pebbles. The humidity should be 50-60% during the growing season (April through September in most areas) and near 100% for several hours each week in winter. Otherwise, this species is surprisingly easy to grow. It usually flowers even when grown under less than optimum conditions.

Soil and Fertilization

Gymnocalycium mihanovichii grows in lean, sandy soil that drains rapidly and does not hold water for long periods. There should be at least some gravel mixed in the soil to increase drainage.

Drainage is so important to this species that the use of containers is strongly discouraged. It is best to plant directly in the ground or in a very coarse, porous container that will allow excess water to drain out quickly.

Gymnocalycium mihanovichii needs little fertilizer during the growing season, and phosphorus should be kept at less than 0.5 ppm throughout the year. This species is not particular about soil pH, but it grows much better if the pH is kept around 6.5-7.0 during the growing season (April through September in most areas).

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Gymnocalycium mihanovichii

This species requires less water than many cactus and succulent species, but it still must have regular watering to grow well. Plants in containers need to be watered 2-3 times each week during the growing season (April through September for most areas). In the winter, water only when the soil becomes dry or if the plant begins to shrink.

If the growing medium is very porous, water will drain out of it quickly. It may be necessary to water several times each week during the hot summer months when plants are actively growing.

Plants in sandy soil that drains well can usually be kept quite dry during winter (October through March for most areas). Keep watering to a minimum whenever the soil becomes slightly dry.


Gymnocalycium mihanovichii can tolerate a minimum temperature of 10°C (50°F) for short periods, but it must not be allowed to freeze. Plants kept outdoors should be mulched in winter to prevent freezing injury.


The humidity should be 50-60% during the growing season and near 100% for several hours each week in winter.

When to repot

Gymnocalycium mihanovichii

Repotting is rarely necessary because Gymnocalycium mihanovichii does not grow very fast or become too large when grown in a sandy, porous mix.

A plant may be forced to undergo major root pruning if it is placed into a container that holds too much water for long periods of time. Root pruning can also occur if the plant is kept too wet for too long.

Sand should be added to the potting mix whenever watering occurs to replace any soil that has been washed away.


Gymnocalycium mihanovichii can be easily transplanted, but this species grows so slowly that new plants do not have to be repotted very often.


Gymnocalycium mihanovichii rarely branch, but they may be forced to make new growth shoots when they are cut back rather hard. Plants grown in containers may require more frequent pruning than those planted directly in the ground.

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The leaves of Gymnocalycium mihanovichii serve as a protective barrier against sunburn. They can be removed from larger plants so that the plant can receive more light if necessary, but the removal of these leaves weakens the plant and may cause it to grow less compactly.

Hardiness zone

Gymnocalycium mihanovichii is thought to be hardy throughout the United States and Canada, although it may suffer some damage during freezes. A few cultivars of this species have been grown outdoors in USDA hardiness zone 7 with success.


The sap of Gymnocalycium mihanovichii is mildly toxic to humans and can cause mild skin irritation.

Pests and diseases

Spider mites occasionally damage plants, but the use of a miticide usually solves this problem. Mealybug infestations can sometimes be a problem in greenhouses where humidity is high.