Young trees. Feed pretty much year round. If it has leaves, it is time to feed. Weakly but weekly. Or if you prefer, less frequently but at a higher dose.
Advanced trees in refinement usually are not fed in spring at all. Here you wait until well after the summer solstice. Until after the bulk of foliage extension and expansion has been finished for the growing season, then you begin feeding. Waiting to feed until this time promotes shorter internodes, smaller leaves and better back budding. You discontinue feeding in autumn, until the resuming following summer.