I have over 100 Poncirus seedling from 7 years old to new seedlings started last fall. None have been pruned as I wanted all possible growth to go toward making a big healthy root. But really, 7 years is a bit much.
I don't think pruning now would be good. I think it would stimulate new growth that wouldn't be well established for winter. Winters here get down to 0 F, or about -18 C.
But come spring, what would be a good plan for pruning? Cut back lower branches, I would guess, as the lowest branches are 1 cm or 2 cm above ground on some of them. Some have been pruned by deer, which I'll be dealing with. And should I not take off too much in one year.
And should I prune those special ones I got for breeding differently than those to be root stocks? The breeders I want to bloom as soon as possible, the root stocks may never bloom, as far as I care.
I'm asking here because it seems Poncirus pruning in zone 6 isn't a hot research topic. If anyone on Earth knows how to do this, here is the best place to look.