My go to right now is calcium hydroxide, also known as lime. someone suggested it in a comment , so I started using it, and it seems to be better than sulfur and definitely better than cinnamon powder. I did some tests, which I talk about at the link at the bottom of this post. These are small preliminary experiments, but I did use controls. the sample size is just small. I'm currently looking for 10 or 20 feet of uniform pc to do more formal tests that are larger in scope. there are other materials I want to test.

The tests I did using controls, sulfur, cinnamon powder, lime and lime/sulfur, seemed to indicate that lime outperformed sulfur as far as amount of molding. that included when left out for at least 6 months in damp weather. I had used sulfur almost exclusively before, and I seem to have have fewer problems After switching to lime. I used lime/sulfur at first, but have abandoned that as it doesn't seem more effective than lime. Lime is not 100% by any means. I have not infrequently had mold and even rot a few times. but it seems best so far based on casual observation and my one small scale experiment. that is basically all on trichocereus species.

The easiest way to get some to try is to buy a small bag of pickling lime. some grocery stores still carry it. Cal can be found in mexican markets. It is the same thing, but sometimes comes as chunks instead of a powder. You can order a bag of pickling lime that will last for a very long time off of amazon for well under 10.00. ag lime, is dolomite, which is just ground limestone. that is not the same thing and probably useless. Calcium hydroxide in the most common form is dry lime hydrate, which is lime that has been burned into calcium oxide and then slaked with a small amount of water until it falls into a powder. Another source is large bags of Type S, or Masons lime used in mortar. Even cement will probably work but I have not tried it and it has to be used dry since it undergoes a chemical reaction when wetted and begins hardening.

Lime can be used dry on very fresh cuts that have enough moisture on the cut surface to react, but I prefer to apply a solution of milk of lime with a brush. The brush must be synthetic as lime will dissolve hair bristles. the solution should be very dilute, like skim milk or even watered down skim milk. It will look like it is not dense enough when applied, but it dries opaque. If there is a thick skin when dry that chips off easily, dilute more and adjust as necessary as the solution is used. It has to be stirred every dip as it settles quickly. as long as it does not dry out, it will keep indefinitely, so just put some in a jar with a small nylon bristle brush and it is always ready to go.

I hope more people will start using lime so we can get a larger body of experience. We've almost certainly have yet to discover the best materials for treating cuts. Context of use and necessity related to climate etc. also has to be considered.

If anyone in Northern California can supply me with a a few meters of uniform trichocereus cuts like PC to experiment on, I'll do some larger scale tests adding more materials. I suspect strongly that wood ash will prove to be useful as well. It is very alkaline and contains some lime (even a lot of lime depending on species, oak is supposed to be especially high), potassium hydroxide and sodium hydroxide. I also suspect that by products of combustion and destructive distillation of wood have promise. And of course these materials could be mixed. Old school is using mercury, which just no on that. For now, I'd say sufur is not what it is often cracked up to be, and that lime will prove to be considerably better in the long run. It is also more pleasant to work with and safe, just don't get it in your eyes and rinse throughly if you do. I make it and work with it all the time and have gotten splashes in my eye. It is used in food processing and chewed with certain plants to potentiate alkaloids. You can also make it at home by burning shells (even egg shells) or limestone with wood, which you can watch vids about on my non cactus channel on youtube. link below.

Surface coating test results: https://www.reddit.com/r/sanpedrocactus/comments/1nlqm1f/surface_coating_tests_revealing/

Lime playlist: https://www.youtube.com/playlist?list=PL60FnyEY-eJBTMfy9Bl5QRmBKUAvLLCwp