Sounds like you have rot on your hands. The worst thing you can do is water a plumeria cutting when it doesn't have roots. I never water until I see the first set of leaves growing.

What you can try to do is to cut the rotten section off. Just make sure that the cuttings has the white sap or it is dead. Let them dry again and make sure there is no rot. Once the cuttings are firm again, I would pot them up again.

Here is a method I learned on the Aloha Plumeria group. Take a whole raw egg and put it in the bottom of your pot, on top of an inch of soil. Then fill the rest of the pot and add your cutting. The plumeris feeds off of the egg, which in turn helps it root.

Good luck and keep us posted.

Andrew

I agree with Andrew, except if you are in the winter season, don't pot it until you have good warm weather. Since you are in Australia, I don't know what season you are in.

Don't try to root a cutting unless it is warm weather - unless you are doing it indoors with lights and heating pad. Being from California, I don't do any of that. Let the forum know if you need help with indoor growing, there are a lot of folks on here that d grow theirs indoors. But with your weather, I would think you will be growing it outside, right?

I too think the soil was too wet. I would recut the ends of your cuttings until you reach green, pristine wood. Then let dry for a week or two. Repot in part commercial potting soil, + at least half perlite, or pumice (or some inorganic product that improves drainage), and don't water! Don't use sand as it doesn't allow enough air in. (You might get by with sand during the hottest time of the year). Keep in warm and bright location and be patient!