I have never trimmed mine.

What are your growing conditions, besides a south window?

Have had this one since the holiday season 5 years ago.....have only repotted once, which was a horrible, horrible mistake. With my track record of murder previously, I thought I'd bring to a florist for the repot. When I got it home from the "professional" repotting it......IT HAD BUGS!!!!! Little tiny flees......I was so mad....couldn't bring it back because it was done by an acquaintance of mine and I felt bad really. So I got some bug killer stuff from the hardware store to add to the soil, added it and the plant is fine now. I only water it once every two weeks. I swear that's it.......I even named it after my friend who recently passed away. She had a cactus that was just awesome......so I did just name it after her. It's only been in the south window for the last year and a half, before it was facing east. really don't know what else to say. Good luck if you attempt it again.

Virtually all soft bodies insects can be killed with it. It's completely harmless to mammals and plants. It kills on contact by smothering the bugs and re-treatment is necessary if one application doesn't get all of them as it doesn't persist on the plant or soil.

Repotting is necessary if the plant is becoming root bound. If you gently pull the plant out of the pot and see roots growing all around the outside, it's time for a bigger pot. It's pretty simple to do as you just buy a pot that's about 1/3rd bigger, gently cut the roots vertically in about 3 places around the exterior of the root ball, place in the bigger pot, and fill with potting soil.

Generally cacti are pretty maintenance free and I wouldn't do anything to it if it's thriving.

adjust growing conditions to make them available for the winter holiday season. If you don't want to induce a dormant period, you can can break off leaf sections that are too long and easily start new plants from those segments.