Gymnocalycium is a genus of about 70 South American species of cacti. The generic name “Gymnocalycium,” from the Greek “naked calyx,” refers to the flower buds bearing no hair or spines. The members of the genus are commonly known as Chin Cactus.
The main distribution area of the genus is Argentina, part of Uruguay, Paraguay, southern Bolivia, and part of Brazil. Most species are relatively small, varying from 2 to 6 inches (5 to 15 cm) in size. In cultivation, they are popular for their easy flowering habits. The flowers are generally brightly colored. Where temperatures fall below 50 °F (10 °C), they must be grown under glass with heat.
Light: Some Gymnocalyciums are shade-seeking in the wild, among shrubs or grasses, while others grow completely exposed. Therefore, some will need light shading from the sun in the hottest months, but to overdo it, will result in the loss of flowers.
Soil: The balance of the potting medium should be sufficient to allow good drainage so that the plants do not sit in soggy soil for more than a day or two after watering.
Water: Watering in the summer while the plants are growing well can be frequent (weekly for small plants in small pots), but always allow the soil to dry out nearly before rewatering. Watering in the winter months at all is unwise and certainly not necessary. The difficult times are spring and fall.