Lots of questions!

1. When would the container be too small for them? When they are rootbound and it becomes very difficult to keep them hydrated. Roots start growing out the bottom of the pot. Problem is you never know when seedlings will bloom. They may not bloom until 6 feet tall. Where do you live and what is your climate like? How much growth do you see each season? Are you in a tropical region or do you have to move these inside for winter

2. What is the ideal permanent container size for plumerias?
I am only 5ft. so I would like to keep them as compact as possible. So, let's say a plumeria blooms at 6ft. Use largest size you are able to move - not clay or ceramic as they are too heavy. Every several years you can root prune and repot them. Or after 5 years or so, you could take cuttings and start over again.

3. Can I chop it off at 3ft and root the top? You could, but a newly rooted cutting will take 2 to 3 years to bloom again. And it could grow 3 to 4 feet before it will bloom, depending on variety.

Will this help both the top and bottom to become compact? The lower part will resprout. Whether it will branch into 1, 2 or 3 tips, depends on variety and vigor of plant. The top, if it has bloomed, will at least be of a maturity to bloom again in a few years.

4. How do others manage their larger collection of plumerias? We don't grow so many of them! LOL! A mature plant can easily take up 36 cubic feet. So multiply that times the number of plants you have. Others plant them in the ground.

Do you up pot every year? Some do repot every year, especially when they are smaller...maybe for the first 4 years or so. Larger plants can be root-pruned and you would use same pot.

5. What is your opinion on those fabric grow bags? I saw one on Amazon for around $7 for a 10 gallon size. Don't have an opinion on that. Seems to me it would be unstable and blow over?

Hi Dave, thanks for answering all my questions so quickly. Regarding #6, I am in trouble because I may be addicted to growing these (and I definitely do not have the space for them). I was already planning on buying some more seeds to try to grow indoors under lights during winter. Yup, I am definitely addicted. Just thinking about them going dormant soon is so sad.
Well, thank you again for sharing your knowledge with me.

I think Dave has got it covered. I tried a fabric pot this year on a Grove Farm Plumeria. its stable, easy to carry, and stores very well. But the plant has under performed this year including dropping inflos and black tipping. Oh and the other thing is the bags are not very forgiving when you get too close with weed eater.

I was considering using these as off season containers for my seasonal in ground plumeria. just concerned how dry they may get for bare rooted plant.
K.

Kms2~ Thanks for telling me about your experience with the fabric bags. Back to searching for another cheaper alternative for those 10+ gallon size pots.

Searching Ebay is the cheapest place for the larger pots that I have found. Even cheaper is to be-friend someone with access to 20 to 30 gallon plastic drums. Cut in half with a jig saw, rope handles can be added for easier handling. A hole saw on a drill puts drain holes in the bottom. Cheap, easy, movable ( with two people!) 10 to 15 gallon pot. Not the prettiest but functional.