Cleistocactus strausii
Silver Torch cactus can thrive in low-nitrogen soil without facing the consequences of low nitrogen. Too much water will make the plant weak and lead to root rot. 
Least Concern. This cactus is locally abundant in its native land and has few local threats to its survival.
This cactus can be propagated by cuttings or seed.
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.