Generally, root pruning is more likely necessary in the opposite of your situation, when a tree is in a pot too small for its size. Small trees in large pots usually do not have circling roots. After removing a plant from a pot, I pull at the bottom edge of the root ball in a few places. Small white fibrous roots are not circling roots and should be left alone. If you feel thick roots along the bottom edge, it is probably best to pull the circling root until you find the point that the root changed direction from vertical to horizontal and cut it above the bend. Sometimes the roots circle higher up. In that case, I use and knife or snippers to cut top-to-bottom vertical slits an inch or so deep into the root ball in 4 or 5 spots. At this point, since your trees have been in the ground for months, it is better to just leave the trees alone.