I repot my snowball cactus for the first time and I saw that there was this long thick part growing under the soil! My cactus has been leaning to one side, so now I know why at least. However, I have no idea why this happened or how to deal with it, so any help would be greatly appreciated :)

I would check if the brown parts are soft. If they are soft, it means that they are probably rotting. To me those parts appear dead.

I am guessing that thick brown part used to be above-ground stem and then somebody buried it in order to improve the stability of the plant, before you ever got it. There are cacti that make really thick roots, but that looks like stem to me, especially given it's covered with a thick fur that looks like spines pushed up against it.

When stem is buried like that, it generally loses its green and turns brown. That is determined by a lack of light primarily. The brown stem is not necessarily dead, though, just a different color. Presumably your plant did okay for a while because the roots at the bottom of the buried stem were doing their job.

In my view it's generally a bad idea to bury cactus stems, at least more than ~1cm or so that might be needed for stability at the time of propagation. The risk is total meltdown due to rot, and that would be accompanied by a softening of the buried area, creeping into the above ground stem, which may become discolored in the process. Loss of stability is often the first sign we have that something may be wrong below ground.

The best and really only option that I see is to cut the top of the stem (the inside of the stem should look entirely healthy at the site of the cut) and then try rooting that. It can be done, maybe not with a real high probability of success, but the key there is patience and not watering much in the beginning (especially not at the very beginning, after you pot up the callused cutting). I can provide more details if you like.

Yes, I was thinking I might need to cut the cactus too, but I was avoiding it because I was worried about the cactus dying in the process. More details would definitely be appreciated!

Baja_Costero said: I am guessing that thick brown part used to be above-ground stem and then somebody buried it in order to improve the stability of the plant, before you ever got it. There are cacti that make really thick roots, but that looks like stem to me, especially given it's covered with a thick fur that looks like spines pushed up against it.

When stem is buried like that, it generally loses its green and turns brown. That is determined by a lack of light primarily. The brown stem is not necessarily dead, though, just a different color. Presumably your plant did okay for a while because the roots at the bottom of the buried stem were doing their job.

In my view it's generally a bad idea to bury cactus stems, at least more than ~1cm or so that might be needed for stability at the time of propagation. The risk is total meltdown due to rot, and that would be accompanied by a softening of the buried area, creeping into the above ground stem, which may become discolored in the process. Loss of stability is often the first sign we have that something may be wrong below ground.

The best and really only option that I see is to cut the top of the stem (the inside of the stem should look entirely healthy at the site of the cut) and then try rooting that. It can be done, maybe not with a real high probability of success, but the key there is patience and not watering much in the beginning (especially not at the very beginning, after you pot up the callused cutting). I can provide more details if you like.