Answer: Unfortunately, while overall health and vigor are certainly important, adding extra nitrogen beyond the basic needs of the tree would not increase blossom production. In fact, an excess of nitrogen can cause excess foliage growth instead. A good time to fertilize is in fall after the leaves have come down, but do not exceed the amounts listed in the label instructions.
To be very honest I suspect the tree is losing blossoms to winter cold -- this variety is very reliable in zone 6 but less so in zone 5 or colder areas. It is also true that a young tree or a newly transplanted tree will not bloom as heavily as a more mature established specimen would, so your tree's performance may improve over time.
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