Cleistocactus strausii
As a houseplant, the Silver Torch cactus is an easy to take care of so long as over-watering is avoided. To naturally simulate the porous effects of the sand in its native habitat, it's important to ensure that excess water will not pool in the soil, causing the roots to become water logged.
This plant’s native habitat does not have winter, but when temperatures drop to the low twenties, it can exhibit signs of tip frost. 
The Silver Torch cactus is most susceptible to 
mealybugs 
and spider mite.
Echinopsis eyriesii
Water the plants well in summer, but let them dry before watering again. Use then special fertilizer for cacti.
In winter keep dry. The temperature may be as low as -7 °C. For flowering in summer, the rest (dry and cold) in winter is necessary.