hello Barbara,
My Brooklyn white that it grown in ground, still has no leaves while hardy chicago have full leaves already and some figlets as well.
I had the same question from others who got the brooklyn white from me. You can fertilize them with slow release fertilizer that's can be 10-15-10 or 20-20-20 such as miracle gro liquid. Only fertilize one or twice early in the growing season. Don't fertilize in August.
It should be fine in this container this year, I would recommend to repot in the fall or late winter next year with miracle gro potting mix and add pine mulch to the mixture.

Bass