I left some seedlings that size in the grow bed last year and they reached 10 ft. In the fall when i dug them up the roots were like long bright yellow snakes thicker than the trunks. Invasive, took over the grow bed. I cut them back severely and put them in grow pots, enough of that nonsense. Rather have control over the root ball as the trunks develop and i train the shape. The good thing is the diameter of the trunk tripled in one year. I started with seeds from a tree in my teachers Bonsai garden. I have seen some nice literati style Wisteria.