Gymnocalycium, commonly called Chin Cactus, is a genus of about 70 South American species of cacti. The genus name Gymnocalycium (from Greek, "naked calyx") refers to the flower buds bearing no hair or spines.
Their main area of distribution is Argentina, part of Uruguay, Paraguay, southern Bolivia and part of Brazil. Most species are rather small varying from 2 to 6 inches (5 to 15 cm) in size. In cultivation they are popular for their easy flowering habits, and the flowers are generally brightly coloured. Where temperatures fall below 50 °F (10 °C) they must be cultivated under glass with heat.
Gymnocalycium plants in general present no problems in cultivation, and will respond well if potted on regularly every two or three years, to make flowering size plants fairly quickly, some within two years from seed, and will provide some of the finest spination in the Cactaceae family.
Light: Some Gymnocalyciums are shade-seeking in the wild, among shrubs or grasses, while others grow completely exposed. Some will therefore need a light shading from the sun in the hottest months, but to overdo this will result in 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 months, while the plants are growing well can be frequent (weekly for small plants in small pots), but always allowing the compost nearly to dry out before rewatering. Watering in the winter months at all is unwise, and certainly not necessary. The difficult times are spring and autumn.
Those species which produce offsets can be readily propagated by cuttings. Gymnocalycium seed germinates well when fresh, and will keep for a few years if stored in cold conditions.
It is not usually necessary to graft Gymnocalyciums, except for chlorophyll-less, or strongly variegated plants, but it may be resorted to in order to grow on seedlings of slow-growing species more quickly or to propagate more easily solitary or cristate plants. Flat grafting seems to be the most commonly used these days, and it really is the easiest to do. The best time for grafting is when both the stock (the bottom part, usually a cereoid cactus) and the scion (the top part, i.e. the Gymnocalycium you are grafting) are actively growing, usually from about April to August.
Pests and Diseases
As much as any other cacti, Gymnocalyciums suffer from the persistent pest, mealybug, in both its forms. Gymnocalyciums, like other cacti will suffer from fungal disorders if overwatered, but often only the root system will collapse, leaving you the job of cutting out any rot in the base of the plant, and dusting with a fungicide powder before rerooting.
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