Cleistocactus strausii
The cactus prefers free draining soils, strong sunlight, but not high temperatures — in fact it can withstand hard frosts down to -10 °C. In its natural habitat it receives plenty of water during the summer, but almost none over the winter. In cultivation, watering too much in winter often leads to root rot.
Lithops
"Lithops" thrive best in a coarse, well-drained substrate. Any soil that retains too much water will cause the plants to burst their skins as they over-expand. Plants grown in strong light will develop hard strongly coloured skins which are resistant to damage and rot, although persistent overwatering will still be fatal. Excessive heat will kill potted plants as they cannot cool themselves by transpiration and rely on staying buried in cool soil below the surface. Commercial growers mix a mild fungicide or weak strength horticultural sulfur into the plants water to prevent rotting. Lithops are sensitive to watering during hot weather, which can cause the plants to rot; in habitat the plants are often dormant when the temperatures are high, doing most of their growing during the cool months of the year. Low light levels will make the plants highly susceptible to rotting and fungal infection.