Tempe can be much warmer than Phoenix. However I have a friend that lives in town around 59 and Thunderbird. She has her trees up against the house and planted in the ground. They have been doing much better since they have been in the ground too. For winter be sure to mulch them, put old style Christmas bulbs on them for added heat and put pool noodles on all of the branches. Frost cloth is nice but you can buy old sheets and blankets at thrift stores. Keep plastic off of them as it will cause damage but you can then cover the sheets or blankets with the plastic.
I think it also depends of what type of plumeria that you have.
It is much colder at our house so everything goes inside for the winter except my oleander pots.
If you don't have them in the ground wait till next year or e mail me and I will connect you with a few friend that are growing plumeria in that area. I'm not sure if I would plant them now or now but your soil is much warmer that in Cave Creek.
I've got three in the ground and have had them there for two winters successfully, and one in a pot that I bring up on my back patio. I do protect the plumies in the ground when freezing temps are forecast: wrap them in rolled up towels (like how you'd fold them after laundry in half like a taco then in half like a taco again) then use duck tap to hold the towels on. For the growing tip I put quilt batting inside a styrofoam cup and tape that on.
Now, they grew like crazy this summer and the towels plan would be ridiculous. So my plan is to get the closed cell foam pipe insulation - it's open on one side has the hole cut in the middle - and tape it around the branches and use the styro cup thing again on the tips.
I pulled them up three years ago and stored them in the garage but for me it was more of a pain than insulating them and leaving them in the ground. Gotta say the insulated look is weird and not for everybody. Will be interested in how others handle this situation. My plumies in the ground grew a lot more than the one in the pot...and one of them blossomed (happy sigh!).
"Hi - Thanks for writing.
Yes, you can plant your plumerias in the ground. I would do it next Spring to get them acclimated the full year.
And yes, they will have to be covered on freezing days in our winters. Anytime the temp goes below 32, there will be frozen plumerias, just like any other plant.
You can cover them with frost cloth, sheets, light them, add a heating element - or you can dig them up and place them in your garage and plant them in the Spring again.
Hope this helps."
So I'm going to leave them in the pots in the location where I intend to plant them in the spring. So I can analyze the sun situation before I commit. Heck, maybe I'll leave them there next all summer too.
I keep the two I have outside all year but I place them on the patio when it gets too cold and it got very cold. 19 degrees cold. I use several sheets to 'seal' the patio with all the frost sensitive plants. They are fine and will go out in their place this weekend.
I am not ignoring you! I just have a nerf ball where mybrain should be, that's all.
I'm kind of surprised- people are telling me what a horrible winter this has been, but with being able to use the shop for the really tender plants and finally having sufficient frost cloths, I consider this to be one of the most glorious winters weather-wise I can remember. For me, not the plants, obviously.