Question
We have a Peruvian apple cactus with one main stack about 6ft tall and one arm (from the base) about 3ft. Location Yuma, AZ.
I have seen/read how big these can get, but it is in a location where we don't want to to get too big. So I want to understand the best way to prune it. I've read about propagating, but didn't understand what happens to a "cut" arm. Does it regrow from the cut point as a single arm, or branchout? Is it better to prune at a joint(narrow part) of an arm, or in the middle (fatter) part. Is there a preferred season to do pruning?, and any treatment to the cut area.

Answer
Hello Gary,
Just to let you know by now, the cactus will not look attractive if arms are cut off. It leaves scars behind. When you cut the arm, the cactus heals by callusing over the wound. It forms a dry substance that stays for as long as the cactus lives. The best time to prune is when the climate in your area doesn't get too hot (spring is best in your area).