Use a loose mineral cactus mix with extra perlite or pumice and clay pots help the plants to dry out between watering. Repotting: The plants need deep pots to accommodate the napiform unit formed by the stem base and the rootstock (or they will often simply crack your pots). Generally, they should be repotted frequently at least every other year in order to provide fresh soil. However, old plants become senile and have a tendency to succumb to disease and a weak root system. At this stage, as is well known, they die suddenly. So, after they reach 10 cm in diameter grow them slowly, and adopt a new repotting period, using intervals of every 3 years. Additionally grow them under drier conditions or with stronger sunlight. However, repotting doesn't necessarily mean they'll need larger containers. Sun Exposure: Partial sun or light shade. They need a good amount of light, a place near the roof of the greenhouse helps drying the pot after watering. Watering: They require moderately watering through the growing season. This can be done weekly during the summertime, if the weather is sunny enough, with a little fertilizer added. Kept this way, plants will show a healthy, although slow growth. Keep dry as soon as the temperature starts dropping in October and keep it perfectly dry in winter at temperatures from 5 to 15 degrees centigrade. Hardiness: Winter care presents no problems at 5°C with plenty of light., but frost hardy to -10°C