Indoor succulent cacti such as Acanthocalycium Thionanthum with its large yellow flowers and Aloe Vera often grown indoors for its medicinal purposes. It produces light purple and green flowers with tall stalks. Concrete, however, produces lime that lowers the water pH. The cactus is very selective in fertilization. Saguaro is thought to be the longest-living cactus. They can grow up 60 to 70 feet high and live for between 150 and 200 years. Cacti love sunlight. They are built for the hot desert sun, and whether living indoors or out must remain in the brightest spot in your yard or house.