The long, snow-white spines on the Mammillaria geminispina make it a stunning cactus, especially in a certain light. In late afternoon when the sun is low, it almost glows. This species freely clumps to about two feet wide. The heads form mounds that seem stacked on top of each other.
My M. geminispina has gone from a pot to the garden, and I'm hoping that a nearby tree will provide it with light shade this summer. The more I look at my placement, the more concerned I am that I may have miscalculated the depth of shade the tree will cast in summer. This cactus takes full sun most everywhere, but in Phoenix, it requires some shade. If I've judged wrong, I may just use a shade cloth rather than relocate it this year.
If grown from seed, M. geminispina can take seven to eight years before flowering, so most collectors buy older specimens rather than wait. Although it is a popular species, it is not easily found, except in cactus nurseries. It is not a reliable bloomer, and the carmine red flowers are somewhat sparse when it does bloom. I really don't think it needs flowers to make it beautiful cactus.