Cactus are interesting plants, you can break one off and stick it in the ground and it will grow no problem. The above photo is my entry for the #monomad Macro Mondays Monochrome photography.
That is exactly what I did for this young cacti. It was growing on the plant below when something nearly broke it off. Probably a bird too heavy for the cacti to support. So I broke it off from the plant and stuck it in the dirt.
It now has roots probably 6 inches long and is doing well on its own.
I recently took them out of their pots and stuck them in the ground. Hopefully they will get a hold before the freeze comes in a few months from now. Ive heard Santa rita cactus are more hardy so hopefully they will, because I want to eat their fruit once it bears. It may be a few years from now but thats an investment im willing to make.
Above is the plant in visual light, the shadows are much longer in visual light interestingly.