5 yrs ago I planted a prunus subhirtella in my yd. A major growth (new shoot) emerged from the graft and has now grown 6-8 ft. Branches that were growing upright are now forming their weeping habit. In spring the top 6-8' does not flower, only the bottom half. Yet the top half leafs out first and looks better than the bottom half (thinned and smaller leaves). Will the tree even out on its own or should I fertilize this fall. Wish I had a pic to show you. Thanks.