After wintering over in an unheated garage, my year-old plumeria looks funky. Do its black tips indicate rot?

Looks like it is getting some rotting. If the rest of the plumie is firm, all the way down, there might still be a chance. You can cut off the black rotted part till you see fresh part and apply some cinnamon to the cut and allow to callus. But got to keep it warm and dry, don't attempt any watering yet.

On the tips that are green, I'd leave it alone, Lisa.

We do have a whole forum on Plumeria, and the real experts are over there. I'd ask @Dutchlady1 for her opinion before you cut off anything.

Here' s the link to the Plumeria forum http://garden.org/forums/view/...

Yes, get as many advice as you can Lisa. Just be aware though that each of our growing environments are different, and like most plants, Plumeria cuttings react differently due to our varying temperatures, humidity and light. Hetty is very, very knowledgeable, I learned a lot from her guidance when I was starting to grow Plumerias too.

The tip closest to the camera looks to be ok. The left tip has had damage but looks like it has sealed over. The back right one is too hard to see.
Is the stem still firm?
Also - is this a rooted plant or a newly rooting cutting?
Please do two things: Unpot it and repot in a better draining mix (mix in perlite); when you do - please fill the pot all the way with soil. These half empty pots are asking for trouble.

Thanks Dutchlady1. This plumie is a year old. Leafed out but has yet to flower. I just repotted it, adding perlite to the potting mix and filling it close to the rim. Stem did feel slightly soft, however. I bet our garage temps got too cold during winter. Keeping my fingers crossed.

Lisa, if your garage was unheated it got about the same temperature as the outside temps. Four years ago I overwintered several dozen plumeria in my unheated garage, no cuttings, all rooted and in pots. We had several days of very unusually low temperatures, down into the low teens, but the biggest problem was that we did not get above freezing for three days. I lost every single plumeria in the garage. I learned my lesson.