Prunus mume -- leaves not growing

Last summer I bought a small Prunus mume 'Beni-Chidori'. I kept it initially in a pot, and it suddenly dropped nearly all its leaves in late summer, before they turned and fell in autumn. I put this down to heat and/or inadequate watering, but I held on to the tree in the hope that it would recover.

During the winter I planted it out into the garden. It blossoms in February, and blossomed reasonably well, so I was hopeful it would do make a good recovery this year. However, I am disappointed now to see that the leaves have appeared only on a few lower branches, and there is little sign of any new leaves elsewhere.

Any solutions -- should I wait and hope it will recover? Prune back severely the parts that are not showing new leaves? Or start again with a new tree?

 

I would scrape the bark with fingernail to see if it is green (thus alive) underneath. I would give it time ... a whole season even ... never can quite tell in situations like this.