I finally had the guts to upgrade the pot for my Mammillaria spinosissima “un pico”. This thing is very prickly! You know your cactus needs a pot upgrade when you give it a ton of water and the pot is bone dry the next day. Apparently my dear Mammillaria was very root bound. The root ball was perfectly intact when I removed it from its old pot.
The first thing I did was to carefully loosen the roots and remove as much soil as I could, especially near the soil line. This makes the cactus very unstable when you repot into fresh soil, but it also allows water to actually penetrate the root ball. This is the first thing I do when I buy a new cactus, as well.
It looks so much happier now! The size of the new pot makes it look so small.