Depending on the weather in March (2018) I am planning on planting our plumeria in the ground during this time.

We have several trees with trunks around 7 inches in circumference and stand taller than 7 feet tall.

What I wold like to do is to plant these, then start cutting them back down to around a foot above ground and placing a good compost around them and see if they will start producing limbs in 2018.

How long should I wait, after placing the trees in the ground before I do a mass pruning?

I would give them a year to get establishwd.

Thanks Hetty - @Dutchlady1

If we planted in March 2018, do you believe that I could take at least a few cuttings in September 2018 (if the trees look well established) ? Then in March 2019 maybe take a few more? My future intention is to get them down to a reasonable size so a frost cover will fit over them from Oct - March only during low temp nights.

My worry is that they will not make it through a full year (with one winter) if they are still this tall and in the ground. At least I could have some cuttings ready for 2019 if in case the tree did not make it.

Your thoughts are very welcome - Thanks

I personally don't like taking cuttings in the fall. They tend to be too green and have less of a chance of rooting than cuttings taken in the spring. But I can see your predicament. You're not actually taking cuttings to root, but reducing the size of the tree. If you are willing to accept that you may lose (some of )the cuttings it is of course totally acceptable to prune your tree in the fall.