Grow lights are essential for succulent and cactus growth in those who don't have a greenhouse or bright, sunny windows. Cacti need direct sunlight. However, if you keep your cactus indoors, it will need to be exposed to 12-14 hours of full-spectrum lighting. You will have to rely on the symptoms that appear on the portions of the plant above ground. Lastly, the hedgehog monkey tail cactus is native to parts of South Africa. Take out the blackened roots to reveal the healthy parts. These beliefs are what make the plant the money tree. Are you concerned about what is happening to the plant?