Growing out bonsai trunks in the ground requires regular maintenance. Create a better Nebari when field growing bonsai trunks. Work the bonsai roots pruning them back which creates taper and ramification in the roots. Then prune back sacrifice branches to avoid big cut marks on bonsai and induce taper and movement in the branches.
After pruning roots and branches it is time to plant the tree back in the ground. Let the tree grow and in 2-4 years it is time to do this all over again.