Plumeria can be rooted by planting the cutting in a good soil mix and a little basic care, but you can get the best results by first callusing the cutting.
Callusing protects the cut end and leads to faster and stronger rooting with less possibility of losing the cutting due to rotting. If left unprotected, bacteria and/or fungus can enter the wound through untreated soil or potting mix, causing the cutting to rot, and because isn't strong enough to fight it, the rot will quickly consume the cutting.
To prevent infection, always use a clean pair clippers to take your cutting, dipping it in rubbing alcohol between each cutting. Once you have taken your cutting, you can sterilize the wound by either dipping the cut end in a hydrogen peroxide or a anti bacterial soap solution, and then seal the end in a rooting hormone powder.
To callous, the plumeria wants to be in a warm, dry environment but will callous better and faster with a good amount of humidity in the air
In SW Florida we usually have high enough humidity that we can just leave them in a dry place outside, but if you don't live in a humid area, you can use a humidity box that can fit 4 to 5 cuttings.
A clear plastic storage box works well because you can generally see what is going on inside the humidity box during the callusing process. This allows you to check moisture content as well as when the callous appears without opening the box. This box is 12” long by 10” wide by 6’ high. The wetted moss will be the source of humidity and the ¾” X 9 ½” PVC tubes will be what the cuttings rest on to keep them from touching the damp moss.
Place your cutting(s) on top of the tubes and place the box in a warm and shady area, a garage or laundry room usually works well. Cutting(s) take about 3 to 7 days to become fully calloused. When the callous is observed, remove the cutting(s) and pot immediately.