I'd like to add to Millet's last post, which is quite correct -- foliar N has been shown to increase bloom on field-grown trees. But I think part of the question may not have been answered -- whether altering fertilizer ratio can affect (or effect!) flowering (or other things, like root growth, cold hardiness, or other aspects of growth) as is often claimed by some fertilizer manufacturers. The answer is no -- all such claims are either misunderstandings of how plant nutrition works, or (more often) direct lies by the fertilizer seller to increase sales.