I have a very young (1-2yr) Beni Kawa that is nice and healthy in a small cedar box. 90% of the tree is about 18" high with nice branching structure. But the central leader started this rapid growth that just won't stop! It's now almost 4' long with no signs of slowing down. It is so thin and spindly that it just wants to fall over if not staked. I don't fertilize it (there was a bit in the potting mix in spring).

Should I trim off this rapid growth or try to stake for a more vertical trunk?? Any suggestions would help. Thnx