CactiGuide.com

I just got some cuttings of Cereus repandus (Peruvian apple cactus), and one of the cuttings is turning black at the cut, almost like rot.

Should I recut it higher up, plant it, what?

Cut it off with a clean, sharp knife higher than the rot. Make sure the cut surface is green and not brown in any areas on the cut surface or it will just rot again.

jmoney's advice is good. I also believe, that a rot has set in. Make sure, that you disinfect the knife with either rubbing alcohol or a bleach solution.
Then place the cactus on its side for a week or so, until a tough skin (callus layer) has formed.
To speed up root formation, you can also apply rooting hormone to the cut surface. I used to dip the fresh cut into a powder of Rootone. This was a fungicide/rooting hormone blend and it worked really well.
Most cacti will readily form roots though. Just ensure, that the callus layer has formed, before placing the cactus stem into a mineral soil, which is best for your plant. You can look up how to prepare a good cactus growing medium by clicking on the tab above in the first row called "Growing Cacti".
Best of luck with your plant.


Harald

I've been using a growing medium of sand, peat, perlite and gravel for my other cacti, so I will use it with this one. This is one out of several cuttings with this species, but it's the only cutting that had an issue. I have it setting right now to callous, it already has a decent callous forming even after 1 day.

Thanks for the help and suggestions!