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.
Bundala National Park
The seeds of the Opuntia cactuses (called Kathu Potak in Sinhala) are spread by macaque monkeys, and perhaps other animals and birds, that eat the fruits. It is also spread by people cutting down the cactus but leaving the cuttings, which then re-sprout. No biological control measures have been carried out with the moth "Cactoblastis cactorum" so far. Manual removal of the cactuses will be impossible as the area where they have spread over is vast.