Rot on cactus cuttings?

[treefingers]

I recently discovered that my favorite cactus developed root rot at the base -- there were originally 3 cacti in one pot. I then noticed that all 3 of the cacti in the pot were infected at various stages (mushy bases and black creeping up the sides) so I removed all of them from the soil and, with consultation from an expert, cut the rot off of all three.
This is what it looked like when I initially spotted the root rot: https://cactiguide.com/forum/download/f ... w&id=50913

For the cuts I sterilized a very sharp knife with isopropyl alcohol and cut 3 inches above the rot for each arm then sprinkled with Sulphur powder. I’m not sure if I was too late in performing this emergency surgery, but I noticed ~4-5 days afterwards that the cuts on all 3 had a black ring around the perimeter of each base then I noticed the black appeared to be slowly spreading up the stems, so upon further consultation, I was told to cut again, and much higher.
First cut: https://cactiguide.com/forum/download/f ... w&id=50914

This is what one of the current cuts looks like after two days of being dried out: https://cactiguide.com/forum/download/f ... w&id=50915. Not sure if it's visible but there is a dark-ish ring around the entire perimeter of the cactus -- this is on all 3 stems.
Are the darkened rings around the cuts normal, or should I assume the rot has spread further than imagined and cut it again? Also, if cut again, how long should I wait until it can be re-potted? Should I wait until I see signs of root regrowth? Is it bad to leave this cactus lying on its side for too long? I feel in over my head here so any advice is welcome.

[hegar]

Looking at the images taken after surgery, I cannot see anything wrong with your plant. The cut seems to have healed fine. A slight discoloration right at the edge of the cut is a physiologically normal occurrence. With the size of plant you do have, you can keep the stem out of the soil for a while, in order to see, if there is still a rot present. It is possible, that the microorganism that caused the rot had managed to spread further into the plant than what the discolored tissue would indicate. Therefor it was a good decision to cut the stem well above the discolored part.
Most of the time, these larger, columnar cacti will easily form roots. One stem of Pachycereus marginatus, which I kept in my office for training purposes, even started to form little knobby roots while standing upright on a table top.
To speed root growth, you could apply a little rooting hormone to the cut end. This substance can be purchased at garden centers, nurseries, etc.

Harald

[greenknight]

Agreed. While it's laying on its side you should turn it frequently so it doesn't bend or grow roots out of the side that's down.

[treefingers]

Thank you for this response, it's very helpful. I guess it will just take time for it to root, provided the rot is still not present. I will get some rooting hormone for the next step.

Looking at the images taken after surgery, I cannot see anything wrong with your plant. The cut seems to have healed fine. A slight discoloration right at the edge of the cut is a physiologically normal occurrence. With the size of plant you do have, you can keep the stem out of the soil for a while, in order to see, if there is still a rot present. It is possible, that the microorganism that caused the rot had managed to spread further into the plant than what the discolored tissue would indicate. Therefor it was a good decision to cut the stem well above the discolored part.
Most of the time, these larger, columnar cacti will easily form roots. One stem of Pachycereus marginatus, which I kept in my office for training purposes, even started to form little knobby roots while standing upright on a table top.
To speed root growth, you could apply a little rooting hormone to the cut end. This substance can be purchased at garden centers, nurseries, etc.

Harald

[treefingers]

Smart; thank you for this tip!

Agreed. While it's laying on its side you should turn it frequently so it doesn't bend or grow roots out of the side that's down.

[ElieEstephane]

May i ask about the species?

[treefingers]

A cereus but I am not sure about the species. It looks like a cereus jamacaru or cereus uruguayanus but I am not 100% certain. Anyone?

[treefingers]

A cereus but I am not sure about the species. It looks like a cereus jamacaru or cereus uruguayanus but I am not 100% certain. Anyone?

May i ask about the species?

[ElieEstephane]

A cereus but I am not sure about the species. It looks like a cereus jamacaru or cereus uruguayanus but I am not 100% certain. Anyone?

Thank you! At least that narrows it down.