Father, what is the warmest the area will be where you will do your rooting, and what is the duration? The 60F minimum is not the problem. In my humble opinion, rooting them will be difficult if you cannot give them strong light and plenty of heat. No moisture is involved though, just light and heat. Is there any access to a rooftop where you live? How about some sort of small patio or a window sill that gets lots of bright light? I am trying to find a way for sun to be on those cuttings. The good thing is that we are now getting into the prime (beginning) cycle of their rooting. Your cuttings might root without strong light and without heat, but it could take quite a long time. I just don't know. All my plumeria have been outside for almost a month, so my only experiences in rooting cuttings is using the outside for that sun and heat.
Maybe there are those who root their cuttings in less than ideal conditions and they can share some tips with you. Unfortunately, plumeria are trees and their genetics are slanted towards those things necessary for trees to thrive.
