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.
Puya dasylirioides
Puya dasylirioides comes from 2300-3300 meter elevation, where the climate is cool all year. It has taken temperatures in the mid-80s (30 °C), but it's possible that it won't thrive in consistently warmer conditions, especially if nights are warm. It is said to have taken winter lows of 19 °F (-7 °C), and might even handle colder temperatures. It grows well in a deep pot in normal cactus soil that contains no lime. Water it deeply occasionally, and avoid letting the soil dry out completely. Some protection from strong afternoon sun might be needed in warmer climates. Over about 40% humidity is recommended.