I thought that compost was a very slow release type of feeding. As long as you are getting good growth, it must be ok. I just wonder if you did some additional you might see a pickup of growth while it's in that box. They tend to really throw big impressive growth if unrestrained and fed well. (in my experience.)No fert. Its planted in a mix of compost pea gravel and perlite. I think theres enough nutrients in the compost to keep it happy. Ive been growing all my in development trees in this mix without issues other than pines. Holds water for two days even in summer but enough aeration to not have root issues.
Will probably repot next year honestly. Still getting roots sorted out. Once that is done, Ill go two or three years mostly unrestrained growth.