Answer: Japanese maples are painfully slow growing and they can take a full year to become adapted to their new homes, so I think that will account for the seeming lack of growth. As for the branching, they may have been damaged during the winter or from a late spring frost. Now that it is summer, I'd prune out the dead branches to encourage healthy new growth and take special care to keep the soil moist but not soggy wet. You might also use a water soluable fertilizer (Miracle-Gro, for instance) to give the tree a boost of nitrogen. One other caution - Japanese maples prefer growing in morning sun and afternoon shade. Full afternoon sun can really stress these trees out.
Hope this information is helpful!
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