We visited Hawaii and I purchased 2 plumeria cuttings. I followed the directions on the packaging and placed the ends in water changing daily. One of them developed rot quite quickly and despite my best efforts and cutting it back to fresh wood several times it "passed away". The second one is thriving with multiple large leaves but I am not getting any roots. I am afraid if I put it in soil it will die. Should I leave it in the water and pray for roots (it has been in water since the end of September) or should I place it in soil and hope for the best?

I have never heard of rooting them in water! If it were mine, I would remove the leaves, cut off the bottom to fresh growth, and let it callus until spring. When weather warms up stick the cutting in a pot of very porous potting soil, and don't water at all until it has grown some roots. It can't support leaves without any roots. We do have a Plumeria forum where you may get different opinions. Scroll down through the list of forums under Communities at the top of the page, and you will find it.

I've never heard of rooting Plumerias (Plumeria) in water either. I no longer have any but whenever I'd root cuttings, it was always as Carol mentioned in her above comments; leave the cut stems out to callous over for 48 hours or so before potting them up into a well draining soil.

Fyi:

https://www.gardeningknowhow.c...

The rooting powder and the watering when potting in that article are both a matter for debate. I just gave my method. I've seen neighbors just take a cutting (in some cases a branched piece two feet tall) and poke it in the ground where it proceeds to grow. They do need heat to grow roots though, so best done in warm weather or on a heat mat.

In warm climates I've just stuck the plumeria cuttings in the ground. They rooted easily. In our cooler climate I root them in soil in pots. I've also rooted them in pots with pure perlite. That worked too. I've never tried them in water. That seems like it would invite rotting.

Some people are successful with water rooting, but most would just root in very well draining soil (at least 1/3 perlite). Bottom heat will speed up the formation of roots so find them a warm spot.