Attila Soos
Omono
In my experience, quince trunks hardly thicken at all.
Yep, frustrating, isn't it. Such a fast-growing species, and no thickening whatsoever.
I have several in the ground, and they never bulk up, after so many years. I think the mistake I made is that I kept pruning them, just like the other trees.
I have a new plan for them this year: I will leave only 3-5 trunks, and let them grow as long as they can - even 6 feet long,without pruning them at all. The only thing I will prune is the shoots from the base.